A priest can have just as much armor with one self buff as a rogue. A warlock has more health/armor/damage reduction then a rogue, a mage normally has just 200 less armor then a rogue. No difference.
Unless you're in plate, armor is a nearly useless stat to consider. A Warlock
can have more damage reduction if they're Demonology specced. Though it's a great spec, it isn't universally the best one to use, so there's a lot of variance. In fact, I'd say they're the rarest breed of warlock.
Like I already said, Rogues are far more viable in melee combat than any caster because they can potentially dodge every other attack that comes their way (in good gear, of course). If you actually consider that, they have way more damage reduction than a Priest, Warlock or Mage.
Show me a rogue/warrior doing 30k white hits and I'll consider.
Hmm... maybe I wasn't clear enough:
it doesn't matter. The mobs that are getting hit for that much are
meant to get hit for that much. Blizzard
designed them to behave that way when a certain event triggers the vunerability. I highly suspect that Rogues can hit for that much. If I can get 500 white crits on mobs, I don't think there's much of a problem if you're in melee range.