I've heard that some PS3 developers aren't compressing shit, and on top of that they're duplicating data in order to cut down on load times. If there's any truth to that, it makes me wonder whether or not MGS4 is following suit.
The funny thing about this is that people are using it as irrefutable proof that the game will never be ported to the 360, as if we never had games that came on multiple disk before, or if with proper compression the game couldn't be trimmed down a bit in size.
