DeltaFree,
I once asked a Physics professor why it was that light behaved a certain way, and tried to couch my question in physically analogeous ways, such as you try with the pressure thing. He commented to me that attempting to draw such analogies was fine as a memory trick, but virtually always fell down when you tried to extend the analogy in any way. He admonished me to stop trying to make such parallels, as they block true understanding.
The old "size of a pea" thing is an example. The Sunday suppliment science reporter can explain anything, and in a few words completely ball up any knowledgable person with analogies like "the energy in a piece of uranuim the size of a pea...."
The EXPLANATION is that the ground effects the airflow around the wing to make it wash outward less, and this reduces the angle of attack of the wing/blade so that more lift is produced at a lesser angle of attack. The effect is to magically make the wing behave as if it were longer, with higher aspect ratio and more efficiency. The lesser angle means less insuced drag, more efficient lift. That EXPLANATION has appeared in about 45 or so posts on this thread. The rotor blade is a wing, and it follows the same rules as it gets close to the ground, of course.
You, DeltaFree then take that EXPLANATION and screw it up with a physical analog that makes you comfortable, you turn it into a pressure argument, and then you feel secure and comfy. That is nice, it is keen, it makes you all warm and fuzzy, and it is wrong, but you should keep it up because the idea of angles of air motion is obviously very uncomfortable for you. In this process of screwing it up, you then insist that your fuzzy little pet story is correct. Please be assured that it is not. Please be assured that the instructor who first said "ground cushion" to you was wrong, in his delightful way. He gave you a simple way to understand that when the ground is near, the helo flies gooder, but he was wrong. Now, in observance of his infallability, you must make all explanations of ground effect fit what you were first told. You were probably the very best student in Sunday school, where faith was the guiding requirement toward understanding. This is not sunday school.
As the last attempt, here is yet again another, separate, more full, complete, different example of a non-pressure explanation of ground effect:
"Ground effects may be explained by the interaction of the aircraft wingtip vortices with the ground. This interaction reduces the strength of these vortices. The weakened wingtip vortices reduce the wing downwash which increases the lift and decreases the induced drag, or drag caused by lift." - Dynamic Ground Effects Flight Test of an F-15 Aircraft, NASA Technical Memorandum 4604 at:
http://www.dfrc.nasa.gov/DTRS/1994/PDF/H-1999.pdf
Forgive me getting crotchity in this post, it must be the pressure I feel with this whole thing ;-)