Haha, i see your thinking.

Yes, not al dirt is removed during foaming, however, provided your using good foam, the amount of dirt left should be a 'film'.

In other word, from a distance (lets say roughly 10 meters) the vehicle would appear pretty much clean, however looking closer you would notice it isn't.

The issue with high pressure rinsing is, that the force of the water that removes and losens the dirt, also forces along the paintwork, and therefor causes (albeit light) damage/swirling.

So to look at it differently, as 2 ways to acheive the same result:

High pressure rinse + snowfoam = light film, ready to wash

Dry dirty car + snowfoam = light film, ready to wash

Dry heavy soiled car + snowfoam x2 = light film, ready to wash.

I just wouldn't risk forcing dirt along paint, as snowfoam is an aid to prevent any need to do so.

Our aim is definately the same, just our methods not lol

Hope you dont mind my long-winded explanation!