Microosft claims the PlayStation 3's 1080p support is just a hype:
Andre Vrignaud, Microsoft's Director of Technical Strategy for XBOX Live says that 1080p is mostly hype with the PlayStation 3. He goes on to say that 99% of the PS3 games released will be rendered at 720p while the only ones with 1080x native support will be arcade ports or games that sacrifice in-game effects. Here's a snippet from Vrignaud's Ozymandias Blog:
The PS3 has roughly the same pixel-pushing capabilities as the Xbox 360. Don't need to take my word for it, it'll be obvious soon enough over the next year. Even if this wasn't the case, consider we now live in a multi-platform development world, and that the current sweet spot developers are targeting is 720p due to the extremely similar system specifications.