Stu, you've got it completely wrong and so has Andy Hamster. We're talking about wfp technology not cars or planes.
If you wfp fast enough, the brush aquaplanes on the glass as the water provides a cushion of sorts. Also, when done at speed, the force of the brush pushing water ahead of it creates a type of minature or micro tsunami which then pushes dirt and debris out the way much more efficiently than just rinsing.
The resin or sap from some types of plants or trees can aid in this process as it breaks down the surface tension of the water. I am at the moment soaking money plant leaves in a barrel of water to experiment.