The Rock did what most other WWE superstars wish they could have done. Look at all of the guys who has been in movies and tv, from Hulk Hogan, to Stone Cold, Kane, Big Show, Triple H, every big name... majority of them bombed and they ended up not seeing anymore film opportunites. The Rock just showed how smart of a business man he is and how multitalented he really is. He took a character, The Rock, who's drive on the success road would have ultimately ended up as "One of the best WWE superstars ever" and his body would have been beat to hell, and turned that into Dwayne Johnson, "A WWE hall of famer(it's a given)/mega movie star" known around the world and not just in the WWE world. He has shown that he can play many different roles. In the beginning of his career, he played ass kicking men who fought with wrestling moves. Scorpion Kings, bounty hunters, ex soldiers or whatever. Now he plays drivers, fairies, killers, shooters, cops, on top of all of that other stuff. Even the person who talks about it the most, John Cena, is trying to follow in Rock's footsteps. But he couldn't, why? because his movies sucked so hard that no one outside of porn and the WWE would offer him a movie role.
John Cena wants to be The Rock. Look at the comparisons, they both came in with one gimmick, changed to another to try to better adjust with the era and the fans, then kissed so much ass that their lips turned shit-green. The eventual heel turn later (which many people are clamouring to happen for Cena) and you're in the same damn boat. Do some movies and then leave, come back, be hated for a while, then be loved more than ever. That's why The Rock, at the height of his career, made a smart business move and went to hollywood. he then came back and people pissed they damn pants out of excitement.
As far as Cena busting his ass for the company, I think he has more to gain from it than the WWE. Cena in himself is possibly bigger than the WWE without him. He's a brand now. Just like The Rock is a brand. Rey Mysterio is a brand. These brands come from the WWE, but aren't tied only to that company. Only dumb, non business savvy guys wouldn't try to benefit from it. Like Punk said, the wheels are gonna keep moving with or without them, so why not expand your own brand? And if Cena gets hurt and can't wrestle, what will he do? Act? Oh wait, he can't. But Dwayne Johnson can land a movie role.
People have to just learn that Cena is The Rock of this era, just with less skills, and less business smarts. You can love him, or hate him, but he's following in the same footsteps. Just like Hogan before them, the list goes on forever.