Games developed at the same time for similar platforms are not a valid basis of comparison when it comes to image quality.
If I'm developing a game for the 360 and for the PS3 at the same time, I'm going to use the same assets. I'm going to be using the same shaders where possible. I'm not going to bust ass to uprez any of my assets. If anything, I'm going to drop the resolution of assets to get them to fit in memory or on the media if there is a problem. But if they're being developed at the same time, the assets are being tuned to the lowest common denominator as part of their creation.
This comparison is like putting the same ingredients into two seperate sausages, cooking them seperately, then comparing the tastes. What's the point?