The latest rumour going around, is that John Cena was the guy who called out Vince for the major decline in the WWE product, as of late. If this is true, then it adds credence to my theory that Cena has filled the role that Undertaker once did - as locker room leader.
Cast your minds back to 04/05, a time where both Randy Orton and John Cena were in the process of being built towards the main event, with the idea that one (perhaps even both) would be the face of the company in the next generation. It could have gone either way intially, but WWE settled upon Cena, for many reasons.
Orton is an erratic individual. Prior to 2007 (when he began to sort himself out), he was prone to getting in trouble on a regular basis. It's well documented that Orton was accused of harrassing former Diva, Amy Webber, to the point she left the company. Orton also had a very well documented substance abuse problem, back in 2006 and has been suspended a further two times since then, after failing drug tests.
On the other hand, Cena is the model employee. His private life is sound (although there is speculation that he had a fling with Mickie James just prior to his marriage) and apart from an apparently amicable divorce, he's as clean as a whistle. There is no evidence to suggest that Cena has ever failed a drugs test, be it in WWE, OVW or his bodybuilding days.
I'd say that a lot of reasons why both men turned out so differently in WWE, is due to the fact that Orton was on Raw and Cena was on Smackdown. Think about it, Cena was surrounded by model employees, who took the professional code seriously, like The Undertaker. Smackdown also had a larger "new wrestler" presence than Raw, and it's well known that the newer guys don't party like the old school guys. In Orton's case, he hung around with Ric Flair and Batista (Flair is legendary for his partying, whilst Batista is prone to moments of lavish partying too) and didn't have the professional enforcement from guys like The Undertaker to keep him straight. Furthermore, Orton and Mark Jindrak would get up to all sorts on the road, and it's not a stretch to imagine that the reason Jindrak's inclusion in Evolution was aborted, was due to the bad influence he and Orton had on each other.