Well I think you will be surprised then.
Note I didn't say the consoles won't be able to output at 1080, just that 1080 won't be the baseline target for all features turned on in individual games.
At 1080 you are using a lot of memory that you could use for other stuff, and people with 720p televisions will not be able to see the difference. Whereas the stuff you do with the extra memory and fill and such at 720 will be visible to everyone.
Basically I'm saying I expect 1080 versions of games to be the 720 version with some knobs turned down, rather than the 720 version being just the 1080 version shrunk. Remember that this gen a lot of games are not 720, even though 720 is the min spec for modern TVs.