I firmly believe the game will be done at least 2 weeks in advance and they're just holding out for the date.
It has to be done more like 6+ weeks in advance in order to manufacture the cases and discs and ship them.
I doubt it will be delayed. The game was said to be very far along last December, though I admit in some of the interviews it sounded like they were trying to cram in as much as they can these last few months.
This is wild speculation on my part, but I'm guessing they need it finished by some time in August so they can then focus on fixing all the known bugs and making sure those bugs don't break anything else. That would give them September to focus on the fixes and October to manufacture the discs and early November to ship them. Granted I'm not sure that's how game releases actually work but that's what I'm guessing.
It's far less common for a game to miss an exact date than it is for a game to miss a targeted release month as well.