Not really. The update is really for those who allready have the game. The average gamer doesnt read gaming news on the internet and therefore the general public will have 0 knowledge of Spec 2. DLC is dlc, every game has that.
Forza 4 should open to a better 1st week then Forza 3 no problem given the expected 90+ average. Sure beats that badge of shame that is the 84 :P