If the Rock wins it cant really be clean. As they've said over and over, after this match, he'll be gone for a while but Cena stays around. Not sure if they want Cena to take a clean loss at WM (see last year), but they really cant have Cena beat the Rock either considering its in Miami and the boo's would be deafening if the home town hero lost, not really the way to leave the show.
Miz interference protects both guys and gives Cena something to do until he gets another championship push likely around the Summer.
DD you mentioned summerslam for the Rock, however he is committed to 2 or 3 movies that will be filming from now until the fall. He probably won't have the time to make an appearance until Survivor Series. I think We see Cena/Punk at Summer Slam this year again.
Miz interference protects both guys and gives Cena something to do until he gets another championship push likely around the Summer.
DD you mentioned summerslam for the Rock, however he is committed to 2 or 3 movies that will be filming from now until the fall. He probably won't have the time to make an appearance until Survivor Series. I think We see Cena/Punk at Summer Slam this year again.