in warwick's original hypothesis, it was stated that the treadmill/conveyor matches the speed of the wheels of the car/plane. so in this instance, the faster you move your arm to push the car, or the more thrust you apply to the plane, the faster the treadmill/conveyor moves, and the vehicle remains stationary
read the first post again, engineering feasabilites are assumed possible, so what drives the treadmill/conveyor and allows it to match speed is irrelevant