Nintendo isn't going to support HDTV (720p and above).
However, it's going to support 480p, and that should be good enough for everyone.

Nintendo has confirmed that at this point in time, they are not supporting HDTV output for the Revolution, however, 480p will be standard. This may mean that the system will be unable to output HDTV at all, or it may mean that HDTV support will be at the developer's discretion.

480p is fine. All this hoopla about needing HDTV on Revolution is dumb.

So yeah as much as the 360 looks absolutely beautiful in HD, I'm definately getting the Nintendo Revolution.