next year is Treyarch year, and I doubt they'll release 2 COD games...what I do see happening is Treyarch release COD:WaW 2, and then the following year releasing COD:MW2 when Infinity Ward releases COD:MW3, assuming of course that COD:MW does well enough.
It's a possibility that Activision wants the wii port to run off the same marketing campaign from COD:MW, it'll be cheaper, rather than make 2 marketing campaigns one for WaW and the other for MW, plus it'll confuse customers.
Take this as you will but this is what I foresee happening.