Exactly as the others have pointed out, people are too obsessed with game engines and numbers that they can attach on to a game. But as long as the game itself feels good and is FUN, its just fine.
What COD needs now is innovation, not necessarily a new game engine. I'm sure a new engine will come with a new console but I do believe that BO2 is bringing a lot of new things to the plate in terms COD gameplay goes.