This is a great opportunity to really elevate a mid-card face.
At Vengeance 2001, Chris Jericho beat Rock and Austin in the same night, and it somewhat catapulted his career.
At NYR 2006, Edge cashed-in his MITB briefcase and it started his main-event career, by ending Cena's 9 months title reign.
-Cena's already won 12 world titles, and has been the alpha dog for 7+ years
-Rock is 40 yrs old, and has wrestled 2 matches in 8+ years... will he even do anything with the WWE after WM 29?
^Why do either of them need this big win, and to be "the guy" to end Punk's nearly 1 year long title reign?
No other face can really get to the top as long as Cena's around, because he's inserted as the superhero into every major storyline.