This could be possible. In many regards this is a great investment by Rockstar.
Remember crucially that GTA4 - part 2 (/ e.g equivalent of GTA3: Vice City) is going to cost much less than GTA4. History would also suggest that GTA4 - part 2 and GTA4 - part 3 will also go on to sell more than GTA4 - part 1.
GTA4 is going to sell well over 10 million copies and make Rockstar / EA, MS and Sony a lot of money. Assuming fairly that it will track above Halo 3's initial sales based on the expanded 360 install base and the entire PS3 install base. GTA4 will sell comfortable over 6 million copies in its first 4 weeks and could conceivably hit 8-10 million within that time frame (1/3 of userbase coupled with people buying a 360 / PS3 entirely for GTA4).







