ORIGINAL: Charlie P.
Well, not quite silly. But the flat bottom certainly makes the throttle able to control lift and so it's possible to trim for level flight and climb with added throttle for easy take-offs. And more importantly, land by lining up with the runway and gradually reducing throttle to bring it in gently.
Take your favorite symetrical wing aerobatic airplane and make it more nose heavy than normal, now adjust the elevator trim to compensate for that nose heaviness during normal (1/2 throttle) cruise. Now see what happens when you add throttle. That's right, it climbs! Now shut the throttle off and, voila!, it goes into a shallow dive.
OK, now move the CG back on your favorite flat bottom wing airplane and see if you can still use the throttle to control lift.
A coincidence does not always mean a cause and effect. We usually only find flat bottom airfoils on trainers and symetrical airfoils on aerobatic airplanes so we assume that the airfoils give these planes their handling properties. That's like assuming that tobacco causes crime after observing that the prison population has a much higher rate of smoking than the population at large.