I don't know of any games that run on 1080P on consoles.
Fallout 3 ran at 720P on the PS3, so I'm guessing it upscales for higher resolutions.
Really? As far as I know, whatever resolution the game supports is what you're going to get. The PS3 will only upscale if you change the setting for it to do so. But if you leave it alone, it'll output the highest the game supports.
Fallout 3 and Oblivion for example only support a max of 720p.
COD4 supports a max of 1080p.