I think we have a better chance of getting challenging AI opponents in a turn-based game, where the program can analyze a static snapshot instead of reacting to developments in real time. This is especially true when you're not up against a single opponent like Warcraft, but a large group of factions that should all be struggling against each other, as well as the player. If I'm playing as Spain and fighting a major war with Britain, I want the AI's full "attention".... not just a 1/50th slice of it, if there are 50 other factions in the game.
I agree.