I once brought up a similar question regarding the non standard resolution (methinks it was that flat hang on the wall LG projector). I was always under the assumption that the mirrors would have to be square as they tilted on their diagonal axis... going by this simplistic logic I'm thinking that the projected image is not going to be true 16:9, hence the screen would not be fully utilised if it is a 16:9 screen, unless the optics somehow squish the image a little to make it 16:9 it could be a consideration for many.
It really does bring into light the fact that eventually 1080p will be the only resolution... hopefully. At least there is none of this PAL and NTSC having differing resolutions, with a unified resolution things should be good
In the meantime 1280x768 makes an interesting transition, however it probably won't sway many away from 1280x720 is my guess, a few, but not many.