Luke you also seem to be confusing the fact that the Match between Hogan & Rock was a match between two contracted full time wrestlers. At the end of the day it doesn't matter who won that match. This match with Cena & Rock may be being built with simalar hype, but Rock is not a full time wrestler anymore. He's coming back for the big pay day, nothing more, nothing less. Kinda like how Hogan came back for those one shot big pay days with Shawn Michaels & Randy Orton.
You can look at this two different ways. The idea behind Rock beating Hogan was a passing of the torch as Hogan would call it. But Hogan didn't pass crap to Rock because again, Hogan left the building the star, and no one left talking about The Rock. So in that view yes, Cena should go over The Rock.
The other way to look at it is as others have said, the WWE has made no quams about having their existing talent lose to people who are only their for one time shots (ie Flyod Mayweather). And although some have said this is different because its the Rock and not a normal celebrity, remember Hogan still came back and beat Orton & HBK despite he wasn't staying just as The Rock isn't staying.
Ultimately as I said before, wins and losses in wrestling don't really mean anything. And again guys like Cena & The Rock don't need to win this match. If Rock wins, what will change? Nothing. Cena will still be their. If Rock wins, what will change? again Nothing. Either way there will be talks of a rematch that may or may not happen.
Also I'm still expecting them to announce The Rock as a HOF inductee for this year. So again, winning or losing the match will mean nothing to either one of them in the long run.