What ? It's common in MMOs. Maybe it didn't work like that in XI, but in every MMOs I've played, it was the tank's duty to pull.
And for the stupid argument starting about "leading" and stuff. I think OP was speaking about the fact that the tank is the only one that decides how much enemies the group will fight at once by pulling 1-2-3 rooms. He's also the only one that decides where the boss is facing, if he stands in the middle of the room or in a corner. He's also the only one that has the possibility to move the fight if needed. There's plenty of things that are written in the tank role that defines it as a leader, not especially a tactical leader, but a battle leader. DPS and healer players can suggest things to the tank such as "you should tank it there" or "can you pull more please ?", but the only role that has the power to decide if he wants to execute these actions or not is the tank. As a tank you're the one that sets the pace. The other roles don't have this kind of power and must follow the tank and suggest him things they want him to do or to change. Leading also doesn't mean giving orders. In a group of people, it is common knowledge that the guy going first is leading. The others are following. It's as simple as that. I think it is completely accurate to say that the tank is leading the battle.