Ignore those examples.
Imagine it this way-
A plane is on a runway(a normal one), and the engines are switched on. The engines basically work by pushing air out the back of them. The plane begins to accelerate and reaches take off speed, and takes off.
Still with me? good. Now imagine this-
A plane is on a giant treadmill, programmed to travel the same speed as the plane.
The planes engines switch on the engines, pushing air out the back, causing the plane to accelerate.
The treadmill tries to stop this, but because the wheels on the plane are free wheeling and in no way connected to the engine, they cannot stop the plane from accelerating. It doesn't matter how fast the treadmill spins, the planes wheels are free wheeling, and therefore will have little effect on how quickly the plane accelerates.
The plane will still be pushing air out the back, causing it to move foward.