In the "Detailing Articles" section here there's an old copy of my "Accumulator's Nonmarring Wash Technique". I really do need to rewrite it sometime...
The whole thing with wash-induced marring is that people press dirt against the paint and then move it (the dirt) under pressure. And having the dirt stuck to your wash medium (even for a few inches of movement before you rise it clean) turns said medium into sandpaper (no, the dirt doesn't really "go up into the nap of the mitt and get safely trapped there" :grinno: ).
Gotta fnd a way to avoid that "moving the dirt under pressure while it's in contact with the paint". The direction shouldn't matter. Not when washing, claying, polishing (consider that Random Orbital polishers move every which way), waxing (same with machine application/buffing), you name it. Yeah, straight-line marring is less obvious than circular/etc. marring (due to the increased viewing angle of the latter), but that's the only real diff.
Marring comes from abrasion. As long as your wash/dry media aren't too coarse (CC-test 'em) it's all about the dirt getting rubbed across the paint.
As for Audis, the only soft ones I've ever heard about were one production run of the Nogarro (?SP? I know that's wrong

) Blue S4s. All others are nice and hard. Forget whose paint is on the Q series, but I just had one as a loaner and it wasn't ususually soft.