Actually, I haven't tried this myself, but I was reading somewhere that one of the improvements of RE5 over RE4 was going to be that you could move and shoot at once. This obviously wasn't the case with the demo, maybe by default the controls are set to the traditional RE4 style. I have been meaning to check the demo to see if there was an option to change them, because I have heard from multiple places that this was suppose to be the case.

The file size difference may just have something to do with the different file systems of the two consoles.