The new AI (normal) has a habit of leaving it's cities empty. And I don't just mean during the first couple of turns either.
In a game that's on turn 18, I have twice now encountered AI cities that were empty. Once this turn (18 and once a few turns ago 14). In both cases the AI had plenty of armies on the map. He just chose to move them all out to make sure they remained grouped together.
Checkout Darklords 151 (55744) to see what I am talking about and notice my battle history this past turn and turn 14 against White.
KGB