I always thought I had a handle on this but now I'm not so sure. The aerofoil is moving not the fluid. Therefore perfectly static air has a velocity relative to the wing surface. The stuff in contact with the top has to get round a longer way so it's velocity relative to the surface of the wing is higher than the velocity, relative to the wing surface, of the stuff underneath. The velocities of the two air streams relative to each other remain the same. If this produces the pressure differential which constitutes the force we call lift then there must be an equal and opposite force. Presumably that's why the the air is deflected downwards. I also thought that the angle of the wing relative to the airflow has a bearing and is why an aerofoil can actually produce lift the wrong way up. The torygraph was talking about a perfectly flat surface at an angle to an airflow deflecting air down and producing a reaction force upwards. Surely all the forces interact to produce lift and have at the same time effect each other. I haven't got a bloody clue!