I guess its time to jump back in, please look at the pressure plot on DJ's link, where the pressure field is plotted. Note that the ground effect plot (the lower one) has higher pressure (darker red color).
Wow, higher pressure for ground effect! But also note that both airfoils are at the same angle of attack. If the lower airfoil were reduced in angle, to compensate for the increased lift due to ground effect, it would have the same pressure distribution.
In fact, please think about it carefully. If the pressure below is greater, the lift would be greater, since the blade area and rpm are a constant. If the lift is greater (due to more pressure) the aircraft would climb.
In other words, the pressure must be the same in all cases where the lift is the same. I.E. the ground effect case has the same pressure below it as the non-ground effect case.