Max AoE targets?

[Toiletzombie]

I was watching a youtube video of some zone (dungeon) and a necro pulled the entire zone and then all were killed by party members that were out of sight, so I don't know what they did. Is this why p1999 made the max AoE rule? I used to play a bard on the server and remember I could get about 40 mobs in OT and hit all of them at once, and now it seems like 20 or so it the cap? What was the cause of them implementing this? Was it like this in normal EQ?