I think they just wanted to hype up the Cena/Punk match for a week to make it seem more special. Which I like, since I've complained before about how so often (seems more than not), the main event of the shows only gets booked when the show itself starts to air, as if kayfabe wise, we're supposed to believe they are going on air without a planned main event already decided. (Hell, that even applies to last night, as The Rock introducing his belt was the 'main event' of the show, and the biggest match beyond that was Shield vs Jericho/Ryback/Sheamus, which was only officially made about an hour before it happened.)
I'm looking forward to the match, as I could see it going either way. If Cena loses via cheating, I could see Vince still entering him into the main event anyway, regardless of how illogical that might seem.