Ubisoft didn't lower their expectations for the game because they changed something in RS2, or whatnot. They lowered their expectations because retailers, like Target, Wal-mart, etc., are shying away from carrying M-rated Wii games, and aren't ordering nearly as many copies as Ubisoft had hoped they would.
The game will be just as good as it always was. You'll just have to find it at GameStop, Amazon, or any such place willing to carry it.