It is all about the angle of attack. Notice that when you fly inverted, you need to add a bit of down elevator to maintain altitude? This isn't because you plane suddenly changed its balance, its because in order to produce lift inverted, you have to raise the nose a bit to increase the angle of attack. I guess in a sense, I might be wrong, that by doing this you are "modifying" the shape or profile (not literally bending) of the wing that is being "presented" to the air? I might not have worded that statement the best in the world, but there is a good thought behind it anyways! Shoot me down if necassary, I'm not an aeronautical engineer.