many games get delayed usually for development issues.I believe that sometimes it is a cunning plan to raise awareness knowing that they will not achieve the originally specified date.My guess is that it will be delayed again and will be released Autumn 2008 as the Xmas run-up is traditionally the busiest period.
You can fit 9gigs on one dual layered dvd and to my knowledge a very small percentage of games even come close to that size so i doubt very much that is a reason for delay.
a few reasons apparently!
1. Due to signed clause with Rockstar, the game has to be launched on all consoles on the same day and as PS3 version is not complete Xbox has to wait.
2. The game is so large that at the moment the only people able to play it on Xbox are those who invested in the hard drive. Microsoft want EVERYONE to be able to play it so some condensing of the gameworld may well be taking place.