AA pilots, in my experience, definitely are prone to leaving the sign on far longer than Delta pilots. It's not uncommon at all for a Delta pilot to turn it off while still ascending (sometimes even shortly after the 10,000 foot mark), whereas on AA it seems to be a matter of reaching cruising altitude and remaining there for 10-20 minutes before turning off the light.

As others note, the net result of that is a tendence to simply disregard the sign.