I've read an article by Dani at videogames.net.au and thought about how interesting it is that I don't even trust release dates the same way as DVD or movie releases are. Grand Theft Auto 4 brings back not-so-sweet memories of the times I had been waiting for a game and told it won't be coming for another month.
The most likely scenario for the push in release date is that they simply haven't finished making the game. Like a student who tries to rush a major on the night before, but this time ain't so lucky