I agree that the 360 has more potential. Alan Wake looks pretty good but I think we will eventually see better.
As for your question, it has a lot to do with dev devotion solely in the graphics department. Just look at Super Mario Galaxy. That game looks amazing and it's on the Wii.
I don't think PS3 developers are doing more to make their games look better than 360's games, they are just making the most out of the hardware.







