A lot of that is those vehicles require special tools that are expensive. Nearly every car needs a 10mm socket to work on it, so every mechanic has a few and in turn they are cheap. Only VW and BMW need a triple square socket, so they are not common and more expensive, and you only work on a few cars that need that so you have to charge more. Mercedes requires all mechanics have a 4 wheel dynamiter and some repairs require the car be on that for calibration making those repairs more expensive. (Note that I haven't been in the business for 15 years so the above is probably out of date)