Not really a myth. Back in the day when these boxes and the 6100 alike was top of the line, several varieties of macs would not boot up with a dead cmos battery installed. Especially if the unit was unplugged from the wall. The power supply on sensing models(no on/off button) will keep the system clock going and the battery is not needed so long as the power from the wall is not interrupted. Once the unit is unplugged for a few minutes thou, it will often fail to show any video. The 6100, and other models that used an on/off switch relied solely on the cmos battery to keep the pram alive and the clock active, so these units would simply not show any video after the chime unless, like was said earlier, a double tap on the power button was used, or a new battery was installed.
Heh, we use to get so many free macs back then because people failed to realize that the unit required a cmos battery. Half the reason I have so many old world units in storage because people would just abandon them, pop in a $15.00 battery and wala! But yes, some units will boot with no cmos battery installed, just how it goes I guess, it's been so long since I worked on these boxes with system 7, the good old days.