Something I've always wondered is how big of a difference does armor really make (other than with cost)?
Defensively, all the difference in the world. It's nice to be able to use the same unit to hold what you've taken, although in my experience generally you don't get continous fronts or much in the way of combat outside of the area of a base when the AI's running things. The engine's not advanced enough I suppose. (I haven't seen a continous front used by the AI in any of the Civ games either, but at least in Civ 3/Civ 4 you get something
like it, i.e. you and they would both end up feeding units into a general area and most of the battles occurred there.)