I don't understand why mass market cars (often by the same manufacturer) get better fuel economy and yet need to be serviced less frequently, then. A Toyota Corolla will do 300k miles fairly easily and yet gets better mileage than a Lexus.
The cynic in me says it's price segmentation. People who buy luxury cars have the disposable income to throw away several thousand a year in repair bills and pay more for gas to boot. In fact, if they buy the car to signal that they have disposable income to burn, it's actually better for their purposes if it has terrible reliability. It shows that they have the means to not care. So it's a win-win-win-win all around: the car manufacturer extracts more for the car, the dealers extract more for service, the luxury car buyer gets to show off their wealth, and the mass market buyer gets a car on razor-thin margins that are subsidized by the luxury buyer.