Meanwhile, the guy who explains the AoEs in the hall of the novice goes:
"An enemy often tips his hand before his big attack, and the best defense is to skip out of the way.", thereby implying that it works more like the swing and projectile animations of action RPGs, which we lack due to... not being an action RPG.

Personally, I crack it up to plain lore/gameplay segregation, much like Nefarian in UBRS yells at his underlings to shred the ones in the robes (aka: Healers) first, only to then obediently follow the aggro mechanic in Blackwing Lair himself.