MortalPlague
Adventurer
They don't have the types because none of them stack. It must have been a nightmare for 3.5 designers when they wanted to make a new feat or class that affected AC; they would have to go through everything with a fine-tooth comb to make sure it wouldn't break the game. And sometimes they'd just miss something, a player would find it, and a new potent combo would bring a problem PC to someone's table.Why not just keep the 3rd edition (yes, 2nd Edition AC in reverse)? If stacking, just be smart about the design, if you look at 5th then you will see they have a ton of AC bonuses from various sources, just that they don't have AC types.
Simplifying the AC numbers cuts down on the min/maxing game. Some people liked looking for bonuses that would add together, searching through various source books for the right combination of feats and items. Others, like myself, would prefer to just have a more streamlined system like 5th Edition.