maybe if I help explain it in 2 parts.

1st. Lets look at the wheels and the conveyor. As the plane moves forward the conveyor moves backwards. Thus negating any movement the plane makes. So if the plane moves or not, the wheels do, esentally nothing.

2nd. With the wheels doing nothing, all we have left to look at is the planes engines making thrust. They do that just fine because they push off the air, not the runway. So with the wheels doing nothing, or something (it doesn't matter) it will still move forward and thus be able to take off.