We can take A LOT more damage than some silly little pet. Our hit-points and damage absorbtion tend to be a lot higher than the pets and minions of hunters and warlocks, plus we have several skills and traits that make us very hard to kill. Honestly, in the end tanking is all were good for, but then again, we're the best at it (some paladins would probably like to argue otherwise, but we'll save that for another thread). You dont have to get very far lvl-wise before you realize that rogues will by far outclass you when it comes to dealing melee damage. Sure, with a nice 2h weapon and the right traits, you can deal out a respectable amount of damage, but in comparison to a rogue of the same lvl, youll end up feeling like youre fighting with a dull over-sized butterknife. On the other hand, while their evasion is good, the rogues durability is a joke, but we on the other hand can absorb a tremendous amount of punishment and survive through situations that would kill a rogue of the same lvl twiceover. So to answer your question in short: warriors are tanks.