Ah, some good Qs there, let's see if I have decent responses.
I think foaming cleaners are working differently from the suds in shampoos, the former being a more active part of the cleaning process (I'm thinking of say...foaming window cleaners or oven cleaner). But yeah, maybe you're right...I just dunno.
I thought that the idea behind a foam cannon (which I've never used) is to get the shampoo to cling better during the dwell-time.
With my foamgun-centric approach, I want liquid soap solution spraying at the point of wash media-to-paint contact, and also flowing through the bristles of the BHB (or nap of the mitt) to flush away the dirt. I'm relying primarily on the mechanical action from the wash media to dislodge the dirt and then the foamgun's output flushes it away. So with those objectives, I want a fairly, uhm...."thin" output from my foamgun, not truly foamy output that would cling.
My only real experience with true foam/extreme sudsing was when I tried "foaming sprayers" with my Rubber Cleaner (tires) and Wheel Cleaner. Got 'em from Griot's. Did *NOT* like them, not at all. Retired them after a few uses.
So I guess I see foam as being about dwell-time, active sudsing in Window/Oven cleaners as being different from what we're discussing when washing cas with carwash shampoo (in the practical sense). Maybe it's just my perspective (based on my somewhat wacky wash methodology), or maybe I'm still missing something here. I can't help but think that "suds" = "bubbles of air, not liquid shampoo that'll clean".
More discussion is welcome..