Are players more stupid than the AI?

This post evolved from yesterday's discussion about the weakness of melee dps in large scale PvP. I had observed that a mage or archer standing back and shooting at people isn't all that likely to get attacked in PvP, while a melee class sticking his head out by running to the frontline is getting targeted by everyone. But has anyone noticed that this is only true for PvP, while in PvE, as long as there are no taunts, mobs will run after the highest thread, wherever he stands? Are players more stupid than the AI in targeting only what is in front of their nose, instead of the ranged dps or healer in the background?