Oddly, this is one of the things I've always liked about Istaria... What semi-sentient creature, in good conscience, would leave its weak or young to defend the outer edges of its habitat while the stronger and more able warriors sit deep inside? It's backwards in most MMOs - the strong should defend the weak.
Now, I understand 'why' this is done - to provide a linear difficulty increase as a player progresses into an area, but it still seems silly if you really think about it.
Istaria's critters also pick on the weakest opponent first, rather than who has the most threat... Again, more realistic - reduce the number of things you have to fight as quickly as possible; but it's certainly a bigger pain to work around in a group.