Hey Phil... I think I understand where your argument is based from.

After a LONG LONG discussion with a coworker..... He intrepreted the question AS

IF the plane wheel speed was matched by the conveyer in opposite direction, **BUT NOT TIED to the speed of the plane**, then there would be 0 movement, and I agree with that, BUT thats not the question that was given to us.

IN THAT circumstance, the treadmill would be able to ACT on the plane by going in reverse @ a very great speed (enough to increase the friction through the wheels) to counteract the planes engine force.

Does this help any??