It wasn't a mistake, you can tell because Cena was posistioning himself to go, he just went without Sheamus pushing him >.< Either way, he was meant to win, WWE need's new stars, so this is the best thing that can happen, plus they wanted a way to bring Orton/Kofi into the title picture, and this does it perfectly IMO.
Wouldn't mind a fatal four way between Sheamus - Cena - Orton - Kofi for the belt, would be a real good match don't you think?