We can assume that some “finishing touches” are why it’s been delayed. It might be that Ubisoft doesn’t want to go up against some of the other big Fall heavy-hitters like Halo 4 and Black Ops 2, though. Dan Hays, game producer at Ubisoft, says otherwise:
Far Cry 3 is a huge offering and we want every element of this insane, action-packed adventure to be of the highest possible quality for the players.
Hey, if that makes Far Cry 3 an even better game, Ubisoft can take all the time it needs. Far Cry 3 will hit stores in North America on December 4th for the Xbox 360, PC, and PS3