I class The Rock as being smart, entertaining WWE after having acting school was a clever way to get himself up, a third generation superstar, a former football player and great on the mike, combination of those three got himself a ticket into WWE and into fame, he knew he would go far with what he had.
Once he reached the pinnacle and went beyond, his calling came because Hollywood saw potential and used him in The Mummy Returns. After continuing to go from strength to strength in WWE and making a world record $55million in his film debut (highest paid debut), he knew he could leave on a high. Because he has millions (and millions) of fans, he knew he would have the necessary film support as people would see his films. Once he was firmly established on his own, he seperated himself from WWE and became Dwayne Johnson. He had the stragety and skills to do it and he's made it his own. I read that he was very popular at the Grammies this year when he presented an award, he's very over in the entertainment industry (outside WWE).
He will probably come back for last match, but that is IF his film career winds down, but at the age of 37/38, he's got a good long way to go in films. He left at the perfect time for him. If I had to be honest, the WWE is a very different place to what we once knew when Rock and Stone Cold were around dominating the leagues, Wrestlemania 20 was really the period where it literally all began again - the rising of Orton, Cena, Batista, the relaunch of Undertaker, that was truly where Rock's time had past. Although his return at the HoF last year was legendary!
I heard that Dwanye Johnson no longer used the name "The Rock" because "the Rock" actually belongs to the WWE, and since he is not signed to WWE anymore, he can't use the name legally. Part of the reason the Rock won't wrestle is because the WWE won't work a contract which allows him wrestling dates, but flexibility to do movies as well i.e. being a actor/wrestler. Vince is apparently annoyed because, when "The Scorpion King" , whihc WWE Films produced, came out, propelling the Rock to mainstream superstardom, Vince naively wanted the Rock to do only movies produced by WWE Films. When Fox, Universal and other studios came knocking with offers, Vince was annoyed because the Rock would get publicity, not WWE. So, the Rock is out of contract, and can only work for WWE when called upon.
I read that Dwayne Johnson was one of the so few superstars who had joint copyright over his wrestling name with WWE, given he was an icon that was made through his own methods and it happened to be through the WWE, I think that if WWE had sole copyright, he would have walked out a long time ago. The reason he dropped The Rock title is because he wants to seperate himself from wrestling. But if you think about it, if WWE had the copyright, they would want him to still be called The Rock, because they would turn to WWE through that name much like Hogan or Austin (though Steve did legally change his name to Austin). To be called Dwayne Johnson is simply saying "I'm not a product or advertisement of WWE".