For football it's a shorter time. Quarterbacks can either stick around for a long time (Farve, Marino, Montegna) or have short but brilliant careers but rarely is one guy at the top of the pile for more then 5-6 years. Other positions are even more fractured time wise. Receivers and tight ends are lucky if they are at the top for more then 3-4 years, then they coast for another few as being among the best, but the peak is only about 3-4 years. Defensive players usually shorter times then that.
Let's look at a few names that aren't on your list
Tom Brady - 12 years so far
Payton Manning - 15 years so far
Jerry Rice - 17 years as a top receiver
Tony Gonzalez - 15 years a s a top TE
Ray Lewis - 16 years as a top MLB
Brian Urlacher - 12 years as a top MLB
Charles Woodson - 15 years so far
Obviously a majority of NFL players don't last long. But the point you seem to be arguing is that ten years at the top is a long time for anyone in any sport, and that players that can make it that long are almost non-existent, and with the exception of Jerry Rice every player I just listed is either active right now or retired within the last year.
I know nothing about baseball, so lets skip to basketball...
Basketball. Aside from the rare exception, it's rare for a basketball player to truly be a star for longer then 4 or 6 years. Yes, the top guys do hang around and are still among the top, but every other year or two you have some new guy come in and become the league and fan focus. Jordan, Shaw, Kobe, Carter, Lebron. Each eventually was or will be replaced as the top guy, although they do stretch out and remain for another few years among the best.
Let's look at the players you named.
Jordan - If we take out the one-year vacation to play baseball, you have fourteen years on top, culminating in his SECOND three-peat fifteen years after he entered the league.
Shaw - I assume you meant Shaq? Sixteen years as a top guy, even while sharing the spotlight with...
Kobe- Really? Seventeen years as a top guy, league MVP in his twelfth season...
Carter - fifteen years...I can give you this one...
Lebron - In his eleventh season right now...he is the current top guy, and has been that top guy for the same length of time as Cena. Who is stepping up to replace him? Carmello Anthony? They were in the same draft class, one and three respectively...
In all sports, the search for the next top guy, the next superstar is constantly happening. EVERY single year, you have to be on the look out for that rare talent that might burst onto the scene. If you aren't looking ahead for the future, then you are behind, even if you are currently at the top of your particular heap.
The funny thing is that I don't disagree with this point at all. You DO constantly have to be looking for your next top star. Where I think we all disagree is on whether the WWE is doing that or not. As several others have pointed out, they keep trying, which is why the landscape looks the way it does right now. The difference between the sports listed above and the WWE is that there is so much more involved with being the top guy in WWE. In football, you need to be able to pass, or catch, or run, or tackle, and to do it better than everyone else who does the same things. But if you have that physical skill, and some longevity, you're set. In basketball, you need to be able to protect the ball, dribble, shoot, and rebound.
In WWE, you have to be able to wrestle, sure, but not even that well. Look at Hogan. He wasn't exactly a technical master, but he could tell a story in the ring (even if it was pretty much the exact same story, every night, for years). To be a top guy, you have to have charisma, you have to capture the interest of the fans, you have to be able to promote yourself, the business, your opponent, and the guy you might be facing next year, just in case. You have to have the physical ability, the mental ability, and the acting ability, and that's just to get a push. It's not enough just to be able to perform at a high level for a long period of time, you actually have to make the fans care enough to see YOU perform. The top guys in the mainstream sports don't put the fans in the seats; the uniform takes care of that part.
When Brett Farve left the Packers (turned heel) Packers fans just turned to Aaron Rodgers and said "You're our champion now," and he replied by doing the discount double check...wow, that analogy worked out really well...the point is, fans pay to see the TEAM, they pay for the logo, the colors, the history, the game...no fan ever went to a Patriots game and said, "If Brady doesn't throw to Edelman we riot!" They go to watch the team, and they hope the team wins. If Kobe goes out and and scores 41 points, but the Lakers lose, the fans aren't happy Kobe had a big night, they're pissed their team lost.When Lebron aired
The Decision, no one complimented him on his promo skills, because basketball isn't about the individual, it's about the team.
Back to the original topic, though...
Assuming Punk leaving isn't a work...so what? Don't get me wrong, I like Punk. But if he is suddenly gone from the WWE for real, I won't miss him. After a few weeks, neither will anyone else, because in the grand scheme he isn't that important. I've been watching wrestling for thirty years now, and in that time only three people leaving have ever surprised me or made a huge impact on the show...Hogan, Stone Cold, and Bret Hart. Hart surprised me more because of the way it happened than anything else. The other two were Hogan and Austin. CM Punk is good, but he is not Hogan or Austin level, nowhere close. The only person in the WWE that is at that level is Cena, like it or not.
Bryan has the potential to get to that point, if handled correctly, but he isn't there yet. Of course, if the IWC had their way, he would never get to that level because his momentum would be killed early by making the worst decision possible...giving him the title.
As far as WCW, there were many things that killed WCW, but the main thing that killed them had nothing to do with the product they were delivering each week. It was the loss of their tv deal due to the Time Warner/AOL merger that truly killed WCW. Even with all of the crap they were putting out in the final year (and I watched it all the way up to the final episode) they were still the highest rated show on the Turner networks right up to the end. To suggest that WWE = WCW in it's death-throes is ludicrous at best...