Anyone who considers flat HTML/CSS pages to be bad form are... part of the problem. There's nothing wrong with simplicity if it suits the content. Pages like drudge report have a format that I like (though I may sometimes find the content offensive :-/ ).
I think I may have mis-typed something. What's considered bad form is simply not using CSS at all. HTML is meant to be a content structuring markup language, not a presentation or design language, which is what CSS is.
Flat HTML/CSS (which is actually what the old personal site I linked is) is fine, but finding that online is pretty uncommon.
To be honest, I think the biggest problem today isn't necessarily the use of javascript or the use of content management systems -- from a client perspective, a simple page on some kind of web CMS is going to be just as easy or difficult to load as a web page in a "flat" or "static" file.
The problems, I'd say, are unnecessary javascript and abusive tracking technologies. On any given modern profit-producing web site, there are probably going to be somewhere from "dozens" to "hundreds" of little bits being loaded and pieces of data being transferred for statistics and ad tracking purposes. This isn't just the single 1x1 JPG/GIF/PNG for like, internal page statistics that Google Analytics made popular a few years ago.
I'd love to use PPC and 68k to browse, but unfortunately things like gmail inbox require that I use a modern browser. I have not yet found a desktop email application that can match the performance and accessibility of Inbox or Gmail. AJAX sites work on these old systems, especially running Firefox on Linux, but are painfully slow. I have to admit, I've never used a G5, and that machine is probably still good if upgraded to Linux or TenFourFox.
Gmail is less of an offender for ad tracking because Google runs it and they're only using their own stuff on it.
In terms of G5s: I honestly have a hard time believing it's going to be a good experience. G5s were often outgunned on benchmarks by regular Pentium 4 PCs at the time, and web benchmarks rely pretty heavily on single threaded performance, and part of what makes the G5 Quad in particular "so fast" is that it literally just doubles up on cores.
I'd have to go find/re-do the numbers, but basically a G5 Quad isn't going to perform well at actually rendering sites. perhaps the biggest advantage it has is its ability to hold sixteen gigs of RAM. If Firefox is being compiled 64-bit for it and it can actually use that RAM, then it has a big leg up on three-year-old tablets.
That said, when I last looked at js performance in tenfourfox (using numbers Cameron Kaiser posted to his blog) it was pretty bad. The iPad "3" and the Surface RT were doing just a little bit better in performance at the time. The real weakness on the iPad 3 and the Surface RT is relatively low RAM for each OS. Windows 8.1 on the RT would be a lot better if Microsoft had put 3 gigs of RAM in, or made it a 64-bit system and put 4-8 in. (Ah well.)
Also, of course, it would just generally be advisable to put a G5 running Mac OS X on the web, because old versions of Mac OS X have known and possibly unknown security vulnerabilities.
On my modern machine, I have 15 tabs open at any given time in Chrome on Linux, and sometimes this uses ~4G of RAM on a laptop that has only a window manager. I've tried things like, netsurf, midori, and other lightweight things, but they just aren't compatible with a lot of things.
It is really interesting how workloads have changed over the past few years. In 2009 when I bought the system (dual core Penryn laptop) that I consider today to be my "main computer" I got it with four gigs of RAM and by and large, a few heatsink re-goops later, it still does everything performantly. Windows and web browsers have actually gotten a lot faster and more efficient.
That said, I have a much faster and beefier desktop at home, a quad i5 sandy bridge system with sixteen gigs of RAM, and each of these systems has a point at which web browsers and spun-out processes (IE and Chrome both do process separation, Safari is 64-bit to start with, and Firefox is slowly becoming 64-bit) will just stop responding well.
It probably depends on the mix of sites you're visiting and whether they're "load and sit" types of pages or "application" pages that must keep network connections open and do work, even in the background.
For better or worse, I definitely see web as the thing driving performance for average computer users over the next few years. In a situation where an otherwise well maintained Windows, Mac, or Linux/UNIX computer with modern/patched software and no hardware failures is honestly probably better today than it was five to ten years ago, it's doing more poorly at web rendering, and just generally, web use has probably gone up over the years.
It'll be interesting to see how this continues to impact the design of systems available to purchase and what systems get advertised as mainstream. Most desktop and laptop CPUs today can turbo boost to gain additional frequency on one or two cores when needed, within a certain thermal limit, and that's probably how we'll see systems with Core M chips (which are quite slow at sustained workloads) do well in more intermittent/bursty web workloads.
Reliable operating system, is seriously the REAL/MAIN issue. But with old OSes 7/8/9 you just gotta live and learn and know what you "Can't Do" or else crash!
Different people seem to have had different experiences with this. I had an iMac/233 from like 2001 to 2003 and then I had a 1.0GHz TiBook.
My experience with Mac OS 8/9 has always been that you need to be very careful about what you do and how you do it when Internet apps are concerned, but that you can pretty easily mix things like Final Cut, Adobe and Macromedia apps, Microsoft Office, even QuarkXPress mostly played nice with other things on the system.
I think the problem is that really big ticket, high end software like that was invested in creating a consistently good user experience, even on a platform where doing so was really difficult, from a technical perspective. (Let's face it, UNIX and NT were miles ahead of System 7/8/9).
Where it really showed was in low-budget Internet applications.. The things I always had the biggest problems with were browsers, simply because they've always been memory hogs relative to the systems they run on, and things like AIM, which just seems to have been unstable.
I think a big part of this is that "web" applications and people having always-on Internet connections where it made sense to run a lot of these things at the same time only came onboard at the tail end of Mac OS 8/9's lives. It's possible that if that idea had permeated in the US earlier (like if the telcos had rolled out ISDN in the late '80s or 45-megabit symmetric fiber in the '90s) then Classic Mac OS may have adapted better or just gotten replaced earlier than it did.
But you are SO right about people who think they can't use PLAIN HTML as "the problem" and the messed up part is that most people just use the new facilities to put top, left, right, and bottom ADs all over the place and videos everywhere! And that's what most of the newer designed pages use the "Latest" and "Greatest" technologies for, which is BS and SAD. Forcing people to get "newer" machines just to browse your flipping ADs!
I think the question is how you fund web sites otherwise. The web is going to be an interesting place over the next few years as we find content creators starting to answer that question.
Of course, the standards commitees also really consider HTML-only web sites to be a problem. HTML is an information markup language, not a design language. If you want it to look good, you use CSS.
There is such a thing as reasonable and minimal CSS, but it's the presentation layer. I think there's an important distinction to be made between "HTML only like it's 1993 and I'm in fifth grade computer period" and "a reasonable HTML+CSS site that looks good, and performs well, and forgoes the worst parts of web advertising.
I don't think this is necessarily a "right tool for the job" kind of situation, as in choosing between modern programming languages to do a task. HTML+CSS is the only tool that exists for this job, unless you simply exit the web and go to an app that makes direct calls to a middleware application, such as the twitter or facebook apps on a smartphone or tablet.
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TL;DR: CSS is an important part of the web, standards committees are who says it's important. That said, statistics and advertising on the web causes a lot of problems and is probably the thing that's most to blame for performance problems and high data usage.