I believe one of the secrets to warrior popularity is, unquestionably, the Arenas. When druids and later paladins took over a chunk of the tanking role, it looked like some warriors, the ones whose gear didn't quite match up to what those classes can do with abilities or who didn't want to spec full protection and limit themselves to just tanking (as well as some warriors who, frankly, just aren't very good at tanking) would probably have to reroll. But then came the arena, and frankly a lot of warriors who would be talented melee DPSers if they could get a spot in raids discovered that they could adapt those talents, gain some new ones, and do damn well in organized PvP.
Are warriors over-represented in arenas? There was a time when I thought so, but the numbers have turned my view around. Warriors are the most played class in the game and the most numerous class at 70. Of course they're heavily represented in the arenas. We should be worried only if they stop being heavily represented there. I don't believe it's a sign of warrior imbalance that they do so well in PvP when partnered with someone who can help keep them alive, it's rather a sign of how mechanics that were originally designed for PvE change and adapt when placed in a PvP arena.
The tanking mechanic for warriors is based around threat generation, which for warriors and bear druids is accomplished through rage generation. The warrior hits his target and generates rage. The warrior is hit by his target, and generates rage. He or she translates that rage into threat generation via static threat abilities and damage. Now, when you turn this on its head and bring a warrior into PvP, with the proper talents and gear, suddenly the warrior is free to turn his rage purely into damage. The warrior hits and is hit, and generates rage. The healer keeps the warrior alive, meaning that damaging the warrior is effectively allowing him to kill you faster. As long as the warrior can avoid snares and other forms of CC or incapacitation, the warrior's only hindrance is in the global cooldown and making sure his 'nanny' (the healer) doesn't go down while he's off playing hero.
Whether it's the mass chaos of AV, the organized chaos of AB and EotS, the annoying running back and forth while carrying a freaking pennant around leaving a glowing trail of WSG or the deathmatch style of the arena, the warrior can usually find a role in the thick of the fighting quite easily because of how this mechanic sustains his or her ability to destroy the opposition. Rage isn't mana, and it's rage that makes the warrior so effective in PvP. Everything else... high armor, high health, high attack power, high crit rates, the various abilities to remove or prevent incapacitation or incapacitate others... these are all delivery vectors. They are means by which the warrior turns your damage back on you. A warrior who cannot hit or is not being hit is already half-dead, a lumbering mass of meat waiting to be carved up.
While I don't think warriors are overly common in arenas because I'd expect to find warriors anywhere in the game, doing anything they can do just because there are so many of them, warriors are still in the minority when taken into account with every oher class out there. Mages and hunters are close to as numerous (very close, in the case of mages) and priests, rogues and warlocks aren't very far behind. It would be foolish and arrogant to assume that there's no interlap: many of those priests, rogues and mages (to arbitrarily grab three classes) are also playing warriors. And warriors are still excellent tanks and PvE DPS in addition to their role in PvP, and not all warriors have the inclination or interest (or, frankly, ability) to PvP at the arena level. I'm just setting foot into the arenas now myself, because my skills are generally much more suited to and accustomed to tanking. If roughly half of warriors are prot specced (as has been alleged) then things have shaken out more or less as the advocates of other classes tanking indicated - those warriors who wished to tank still do, and those that did not moved into DPS or PvP roles.
I can't say I really see a problem here, unless the problem is success. Despite numerous changes, nerfs, and re-alignments the warrior class is as popular now as it has ever been. Warriors are main-tanking in raids, putting out DPS in instances like Shattered Halls and Black Morass, and PvPing in battlegrounds and arenas. The flaws and limitations of the class (and yes, there are both, nothing's perfect) don't get in the way of the enjoyment players seem to find in it: I know that for myself few things equal the rush I feel when I pull aggro off of a mage who is about to die and drag a mob back over to where it is supposed to be.
As long as warriors continue to be fun to play and offer a variety of options, as long as rage frees warriors from the annoying busywork of the mana classes, I expect they'll continue to be among the most popular classes in the game. Warriors offer a chance to play something different in terms of game mechanics yet familiar to everyone who has ever read Robert E. Howard or heard of Beowulf, Siegfreid or Arthur, and I for one will always play them as long as I play WoW.
I'm just glad to find out that so many of you have such good taste.
Next week: Patch 2.3 will be here, and I'll be covering warriors from 20 to 40. I may even roll a new warrior and see how long it takes me to get to 40 with him or her once the patch hits.