The "19 seats or less" exception is why the smaller commuter turboprops generally had exactly 19 seats, like the Fairchild Swearingen Metroliner, the BAe Jetstream 31 and the Beech 1900.
As to the UM policy of the new AA, here is a thread from another forum where an employee claims that the US policy is moving toward the AA policy:
http://www.airlineforums.com/topic/5...mal/?p=1048436