Machinbird,
Good article. But why only the trailing vortices and not the 'bound' vortex from wing tip to wing tip?
Reminds me of how 'ground effect' is modeled in CFD. Imagine an identical airplane upside down below the first one, so that the ground surface is the plane of symmetry between the two (don't ask how the mirror airplane deals with gravity, just consider the flow disturbance it creates for the first airplane). Since there can be no flow across a plane of symmetry (it wouldn't be symmetric otherwise), the airflow encountered by the first airplane is identical to that above ground surface.