Having 10x the space means nothing if you can't access the assets you need.
You need to remember that storage space means little when it comes to graphics, dual layer discs are more then enough for any game, even if it means shipping on multiples.

The ps3 only has 256+256MB of RAM, while the x360 has 512+10mb's, the reason why dev's complain about ps3 being hard to develop for isn't just cause of the cell, but also very strongly cause of the divided memory, extra pipelines need to be build into an engine before the video processor of the ps3 can access the full 512mb's of ram.
And even then, the 10mb embedded ram of the 360 provides a huge framebuffer for extra stuff, like free 2xaa or other effects.

Couple that with the fact that the ps3 OS uses a much bigger chunk of memory then the 360 OS, and you simply don't have the amount of ram to work with to make them look identical.

But back to capcom, they are not exclusive to any system, since their engine is, in the first place, a pc engine and I very much doubt microsoft paid them for anything, I mean just cause the attendant said the 360build looks nicer, doesn't mean they got paid to dumb down anything. That would actually make Capcom look bad instead of ms.

And in that same article it's actually said the later levels looked identical, so the demo levels for the ps3 were just some older code.
DMC4 looked nearly identical on both systems, only if you would really look for it, one would notice x360 having a slight edge in image sharpness. But other then that Capcom did a fantastic job of showing they aren't partial to any one system, RE5 won't be any different.