"We have extensive DLC available from the first day and are planning to release new content every other week over several months," Bouda said. This experimental model lends itself to the game, he said, because the game is about "environments, tracks and vehicles – not about a continuing story, like Homefront and Saints Row."
Of course, if this experiment ends up being successful for THQ on consoles then it's anyone's game. See: EA's Project Ten Dollar.
Update: THQ has slightly revised its previous statement of "every other week" for the game's DLC. Bouda contacted Joystiq to say, "We are targeting several drops within each month over the next few months starting day one."