Hmm.. could probably stand more interesting behavior tweaking, but my experience so far (at least when it come to surface critters) is that Aggressive is more "mostly" than "always".
Sure, most of the time my encounters with bears/wolves end with them chasing and/or killing me.. but still have had more than a few encounters where the wolf snarled at me and continued on its way (though I didn't stick around to see if it would change its mind). Even (twice I think) been chasing a rabbit/racoon run through a bush to find I was now chasing a bear.. and wisely let him have the critter and ran back the other way..
So, it seems there may be some less hostile quirks to their behavior already, just a bit on the rare side,.. or I just got lucky with some glitches or something