Because if its diverting flow in any direction, there has to be a resultant force as a result of Newtons Laws Surely.
It interests me, as I wonder how CFD software predicts lift ... As someone has mentioned, without viscocity, you cant get assymetric flow, thus without Newton, a flat plate could not produce lift.
It would be interesting to see what effects this would have on a flat plate in superfluid flow (0 viscosity).