I'm fairly certain that the reasons for changes in the graphics, etc. are not entirely due to the 360 not being up to the task.
My guess is that there have been other constraints, some perhaps even PS3 limitations, that have caused this downgrade to occur. Remember, you're looking at screenshots without REALLY knowing the story behind *why* things are being done a certain way.
Naturally you can't blame other circumstances or the PS3 itself... it has to be the piece-o'-trash 360 that's to blame.