It seems to me that the "will take off" crowd is right...IF the plane was already airborne. But to get airborne, it must move forward relative to the ground and surrounding air. It's not doing that on the belt, just like the runner on the treadmill doesn't advance relative to the room.

I think whoever said the question of what speed means in this instance is right. Can the belt really "match" the plane's speed, and if so, what exactly does that mean? To me it means it negates the plane's forward motion, just like a dyno does to a car or a grocery store conveyor does to an orange.