John,
I don't think that any of the posters have disagreed with the information on your referenced web page.
But; ~
- This web page does not disprove 'pressure'.
- Bell has said that 'pressure' on the underside of the fuselage contributes to ground effect. This is a third reason, which is in addition to the two that were mentioned on the page.
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Quote from your referenced web page;
"First and most important is the reduction of the velocity of the induced airflow. Since the ground interrupts the airflow under the helicopter, the entire flow is altered. This reduces downward velocity of the induced flow.
The above is a superficial answer.
What enables the rotor to produce a lesser velocity, and yet, produce the same lift?
OK it's the ground, but, the air is the only connection between the helicopter and the ground.
What change has taken place to the air?
More camel dung added 