Xbox 360 supports 1080p as well.

Because of the extremely large amount of bandwidth available both between the parent and daughter die as well as between the embedded DRAM and its FPUs, multi-sample AA is essentially free at 720p and 1080p in the Xbox 360. If you’re wondering why Microsoft is insisting that all games will have AA enabled, this is why.

ATI did clarify that although Microsoft isn’t targetting 1080p (1920 x 1080) as a resolution for games, their GPU would be able to handle the resolution with 4X AA enabled at no performance penalty.