Wow. There it is:
American Airlines AAdvantageŽ members and oneworld top tier status holders, regardless of their tier status, cannot access lounges when travelling solely on North American itineraries within or between the U.S., Canada, Mexico (except Mexico City), the Bahamas, Bermuda and the Caribbean.
http://www.oneworld.com/ffp/lounge-access/
Unless I'm reading it wrong.