True...and if people thought about it they would see this is true. Air must flow along the top of a wing and then be sent downward. The bottom of the wing of course "rides" along air like a boat on water. These two things cause air to go down and the plane to go up. Every pilot knows if you hit the relative air at a critical angle the air on top of the wing will stop "sticking" and seperate from the wing...this is called a stall...and you won't have flight anymore. Also...frost on the top side of the wing will cause the air not to stick to the wing...and you can't fly in that case either. So we see easily it is not some magical pressure differential that is "sucking" the plane up.