They may also get some morale bonuses and fatigue bonuses, but as far as I know, the only bonuses are to stats. The AI is no smarter (which is why you can beat an army with +9 attack and unbreakable morale), it just is more killy.

I'm almost positive that both sides have "basic" stats on medium, while the player gets some stat bonuses on Easy. So I have to disagree, CR.
The ai does not get any boosts to it's attack stats on any difficulty level, and the increased effects of morale and fatique affect both.