Interesting thread. For the past few months I've been flying DCA-ALB-DCA aboard CR7s and CR9s in F (in addition to all my business travel on DL), and the AA GA's are always trying to get my wife and daughter to gatecheck backpacks that just happen to have wheels but which absolutely fit under the seat in front. The reaction has ranged from being miffed at our desire to take the backpacks aboard to downright hostility that we were insisting the bags do fit under the seats. The girls started putting the backpacks on their shoulders instead of rolling them down the jet bridge to avoid a confrontation. I figured it was an AA policy/culture sort of thing...