I think it was generally expected that if you had the money to buy a Mac tower which were the flagship models, then you were likely going to want to bu some decent speakers anyway, or were going to be using it in a specific application where it didnt matter... realistically the only reason they have a speaker is that it's not acceptable to sell a computer without one. lol
Most of the pro machines right up to the last tower MacPros had pretty woeful onboard speakers for this reason, whilst lower end machines such as AIO Performas and iMacs etc, had pretty decent speakers in them as whilst they werent cheap as such, nor were they marketted as such speciically, they were intended for a consumer who had different ideas about what they needed in a computer. Professionals wanted powerful machines that they were able to expand, customise, and upgrade to grow abreast of their changing needs, and didnt want to be paying for redundant things when they were already paying top dollar for a workhorse... this is part of the reason the 9600 for instance and all towers after it dont have any onboard video controller. The average person however often cannot see any value in having 5 empty PCI slots and 2 empty drive bays, yet not even being able to listen to Celine Dion without spending more money again on some beearable speakers... this is where the Performas started and the iMac continued. They had the things the average person wanted and minimal stuff they didnt need... Hence why a $1000 iMac G3 has beautiful HK stereo speakers and a modem, whilst the $4000 G4 of the same era had a crummy paper speaker and you paid extra for a dialup modem.
