Basically, I'll go with what the Reverend and Wajeff said below. I might
emphasize that the Rohirrim didn't have much chance to show the orcs any mercy,
since those that didn't get run down directly ran into the woods.
Also, I don't think the Huorns are quite as glaring of a deus ex
machina as they might be--Gandalf rode hard and fast to get them into the fray,
and they arrived with time to spare. History is repleat with examples of
reinforcements arriving late in a battle to sway the course of
things.
Matthew/Ugluk
http://www.larp.com/orcs/
