1UP recently interviewed Rockstar's Sam Houser. You should probably go read the whole thing, as it touches on some interesting stuff, but one thing's probably more interesting than the rest. It's where Houser says what we've been saying for a long time now: the 360 needs to sort out the issue of its non-compulsory HDD usage:
One of the problems with the 360, and it affects games like Grand Theft Auto if you think about how much content we put in the actual machine, is the fact that they don't have a significantly larger storage medium than the previous systems.
You're damn right, and-oh. You're not done.
I think that the 360 is going to have to get 'round this issue we're talking about. I can think of various ways they can do it. Hopefully, they're going to adopt one of those in the next year or so, because it's going to become more of an issue. If we're filling up the disc right now, where are we going? It's not like our games are going to get any smaller. I think that issue's on the table with a bunch of games right now. I'm sure they'll come through with an intelligent solution.
Hope he's right. Also hope GTA IV wasn't "affected" in the most literal sense of the word. Motormouth: A GTA Q&A [1UP]