Dunno, if the argument is that somehow by accident the fact that spawning points for enemies were set high in the air, due to a programming mistake ... and that dozens of instances of this (thing is, Realmz, it constantly keeps happening) slipped through beta testing ... I'm not sure I believe that.
No, I think the combat design team decided on it as a mechanic, and from what I've heard, it wasn't just for keeping players on their toes; it also apparently had to do with stability issues, problems with too many enemies being onscreen at once. So has been passed through the grapevine, anyway.
Still, as I said elsewhere, if one rabid critter drops out of the sky and attacks you, just for nostalgic-da2 lulz in DAI, well I could dig it.