Before WoW, I played a lot of pen and paper RPG's, and the one thing that always stayed the same about them when compared to games like World of Warcraft or its MMO antecedents is that, in most pen and paper games, there is no mechanism for roles like 'tank' or 'dps'. There would usually be a healer of some kind or another, but in a tabletop RPG no one cares if the strongest melee combatant in the party is a holy paladin, a brutal sword-swinging warrior or a stealthy rogue, and whether or not any of them did more damage to the monster than, say, the wizard would be totally irrelevant. There was certainly no mechanism in the rules to keep a monster or monsters attention fixed on the guy with the most health or armor, either. So when I first started playing WoW I had no idea that my first character, a paladin, would be asked to heal people nor what 'tanking' even was. And since I was playing it at the time it first came out with other folks new to the game, no one bothered to explain to me what tanking was because none of my friends knew, either.
It wasn't until my first Scarlet Monastery run that I even realized I was supposed to do something there besides just hit things. Now, MMO's like WoW are so popular that the oldest pen and paper RPG is trying to learn from them, including incorporating how the various classes work in combat to some degree. It's all gone full circle, I guess - the first MMO's seemed determined to be D&D, and now D&D is becoming more like an MMO.
Did you immediately understand what you would be expected to do in a party? Did you accept it or reject it? And do you think it will translate into offline play? I went out and bought every book for the World of Warcraft Roleplaying Game but I never tried to actually run it... maybe I was just behind the times.