Yes, and that's what is so amazing about the people that suck so incredibly bad at an instance as easy as Deadmines.
Can they even tie their shoes? Have they ever played a computer game that requires using a mouse AND keyboard at the same time?
I think a lot of veteran MMO players underestimate or forget how unique the aggro mechanism is. Most non-MMO games (and real life, for that matter) use positioning instead of aggro to determine how fights work. I cannot think of a single-player game which really has the same concepts.
Most games: The dragon does not attack the priest because the warrior is blocking the way.
MMORPGs: The dragon does not attack the priest because the warrior has more 'threat'.
The first time you do Deadmines is often the first time you are really exposed to the tank-healer-dps trinity that is at the heart of current MMORPGs. Previously, you've been soloing, or fighting mobs where straight-out dps is a solid tactic.
I know that it took me a great while to truely understand it. WoW is the first game I've played that used aggro-based mechanisms. I played a warrior first, and the concept that 'threat' is different than--but linked to--'damage' was hard to really grasp.