@Phoenix_Wiight: First of all, I don't have SA, so you're wrong. Second, by your logic, no one should have bought GTAIV at all because they've already seen Liberty City in GTAIII -_-
@Darth_evidem, CaptainPreferences, and Stockstar: itcould easily be done on 3-4 gbs.
-The ISO for the pirated version of GTAIV was 6.4 gb.
-The expansion wouldn't include the game engine, which is a gb or two right there.
-Second, since it's an expansion instead of a full game, it likely wouldn't have as much in the way of new dialogue and cutscenes (there would be new plot obviously, and maybe new girlfriends, but possibly half as much as the main game, or 75%).
-The city probably wouldn't be as large as Liberty City (I know it was in the SA game, but whenever R* reuses a city they completely redesign it). It'd probably be 60-70% as big, which cuts down on extra textures and models.
So, it could fit quite easily on 3-4gbs.
This actually makes a lot of sense to me, as Microsoft, while sometimes... generous... with their money, doesn't pay $50 million for a mission and two new guns.