Thanks for opening my eyes. Apparently this is a case of Heinlein's "Any sufficiently advanced technology will be indistinguishable from magic."

From what I've found so far:

Stainless brake lines are in fact not made with copper. However, most automobile brake lines are made from "Bundy tubing" which is NOT stainless and in fact is a copper-clad cheap steel that is rolled into a tube.

Apparently copper contamination only occurs in Bundy tubing, which is what most but not all manufacturers use. (It is cheaper than stainless.)

The problem with copper contamination is also fairly new. Copper generally would protect baser metals from galvanic corrosion, but apparently in new cars with ABS systems, it plates out around the ABS system seals--and that's the problem with copper contamination. If your car has Bundy tubing and an ABS system, that combination and that combination only have a "copper problem". Which would be many or most modern cars.

The copper contamination itself apparently is from corrosion inhibitors in the brake fluid wearing out--the same problem that radiator antifreeze has. Yes, an "iron" engine block will get some nasty internal rust and the radiator and heater core will corrode (and there can be fast failure on any soldered seams) if the corrosion inhibitors wear out, as most do. This is not because of the glycol--but because there's some water and other minerals present even in "new" glycol systems.

Which also begs the question: Do our cars have stainless steel brake lines, making copper contamination highly unlikely? Or do they use the cheaper Bundy tubing?

I will have to severely admonish Audi if they built a "high technology" car with Bundy tubing! That is 1930's technology, it is inexcusable in a high end product today.