100 watts is also enough to power a Laptop or a Mac Mini. I can't wait for the day when you just plug one cable into your laptop for power, video, and everything else. (Provided your external monitor has a USB hub.) Docks will be obsolete.
I sure hope power provision is part of a negotiation protocol; using existing form factors to provide power has been disastrous in times past (e.g. Amiga 1000).