And by "other melee classes" I mean "other than Feral Druids and Death Knights". The only reason Warriors don't make them obsolete is because of the utility those classes bring. However, the Death Knight is VERY close to being in the aforementioned "obsolete" category.
Having said that, in what PvP situation would you rather have a Rogue, Enhancement Shaman, or Ret Paladin? What major impact can those classes have on an encounter that a Warrior doesn't just outshine with their massive damage, multiple teleports to target, the best escape ability ever conceived (Heroic Leap), the second-best escape ability (Intervene), spammable anti-stealth, the second-best snare in the game, decent passive life regeneration when under attack... I'll stop there; I think we get the picture.
For as much as people complain about Feral mobility, it's absolutely nothing like a Warrior's. Ferals can break roots and snares by shifting repeatedly, but a Warrior doesn't care one bit about snares -- they barely affect their performance.
For as much as people complain about Feral self-healing, Warriors have just as much -- except it's totally passive. Ferals have to shift out to take advantage of Predatory Strikes procs, and Leader of the Pack is a ~8k heal on a 6-second cooldown that requires the Druid to land a crit (i.e. actually be attacking something). Warrior healing simply happens whenever you attack them, and gets even more powerful if you root or stun them. All the complaints about Feral bleeds, yet I have put a Mangle, Rake, and 5CP Rip on a Warrior, gone Bear to tank her, and watched her HP go UP as she attacked me (I made the grave mistake of hitting her with a Bash, it seems).
All that mobility and damage makes it hard to come up with a reason to even bring a Death Knight. Why Strangulate a caster when you can just have a Warrior tunnel vision them? Holy Paladin? No problem! Build a full Rage bar, Colossus Smash, and unload. Did the Paladin bubble to get a moment's peace? Warriors have a solution to that too.
Putting aside Feral Druids and their wonderful utility and CC... why bring any other melee besides Warriors to PvP these days?