Those guys are the five with the greatest marketing power at the moment.
This is the center of the argument.
Like these guys or not, Cena, Orton, and Sheamus are over with the "casual crowd" and people buy their gear. John Cena is the biggest merch mover of all time, Orton is loved by women who think he's sexy, and Sheamus is, as JC said, a cartoon character. Kids think he's awesome. That's also a big reason why his character hasn't really developed at all since he turned face. Children like simple characters.
Reigns is the future central babyface of the company. He's the "next big thing".
Bryan is the most interesting because he "shouldn't" be so popular. There have been a lot of comparisons between him and other guys from the past (Jericho and HBK seem to be the most popular, although that usually gets the knee-jerk "He's no HBK/Y2J and you're stupid for saying so...durrr!" response), but I think WWE sees him as a lot like Mick Foley. He doesn't have a great look, but he's got definite in-ring ability, an unmistakable charisma, he's tough as they come (although not quite as insane about it as Foley was in his prime), and his mic skills are excellent (I can hear the teeth-grinding from some of you on that...but it's true). Add to those his indy cred (remember Foley's "King of the Deathmatch" title, which he won from Terry Funk), and I'm betting that's what they figure they've got....only moreso. And I think they're going to give him a little more room to run with the ball since the audience is so into him.
As for Cesaro, Wyatt, Ziggler, Rollins, etc., etc., this list doesn't suggest that these guys won't be big someday or even in the near future. It's just who they think will be the biggest guys they can build upon after Mania. In 5 years, that list is probably Reigns, Bryan, Cesaro, Dallas, and Rollins. Or there could be three or four (or even five) other guys on that list then.
wk
: He does suck thou
