With ADC, Apple had to shunt an extra 28V through the MB to power the screen. There were few manufacturers who wanted to mess with it, and yea, DVI became the standard. Plus, they couldn't figure out how to put ADC on the laptops, so it was a major pain to use an ACD with a PowerBook.
As for the PowerButton on the Keyboard... That lasted from 1994 to 2001 (as the Cube, and it's extended keyboard dropped it). On the USB keyboards, you could not use the power button to restart the comptuer, like you could on ADB keyboards (that is one reason many people with B&W PowerMac G3s use ADB keyboards. Also, it was one of the later PowerMacs (and iMac G4/Alu PowerBook) that removed the circuitry from the computer to work with the PowerButton. Considering so many PCs can now be turned on from the keyboard, it seems like something that Apple should bring back, using the trianular symbol, or as I called it the "Jo-ke-nin" (from a dream). Also, remember you can use various key combinations on the keyboard along with the eject button to regain some of the functionally of the power button, like bringing up the "special" dialog (so you can put the computer to sleep, restart, or shutdown).
TEG