There are very few titles on the PS3 that run in true 1080p and even fewer on the Xbox 360. While a game like Gran Turismo 5 isn't 1920x1080 it is technically 1080p. The game is rendered at 1280x1080 with a widescreen field of view and the game is then stretched to fit 1920x1080 which actually does make the game look noticeably better than 720p, but it isn't really the same as TRUE 1080p. There are quite a few downloadable titles on the PS3 that run in TRUE 1080p, but they are mostly games similar to what would be found on the Xbox Live Arcade. The 360's biggest problem with doing true 1080p is probably the fact that the 10MB of embedded eDRAM that is used as a frame buffer was designed with 720p specifically in mind. Had it been larger, it would it would likely be better for 1080p gaming than the PS3 is.
One thing that is nice about the 360 though is the hardware upscaling so if your TV is set to 1080p, EVERYTHING is upscaled to 1080p. On the PS3, if the developer doesn't specifically make it so the game upscales to 1080p and it is natively 720p, the output resolution will be 720p. It's not really a big deal in that specific case, but say you have an older TV that only supports 1080i and 480p, your 360 will scale 720p to 1080i but the PS3 will only do it if the developer decides to implement it.