Highly unscientific anecdotal evidence and personal experience living in an area with an unusually high concentration of such cars shows me that most people that own really fast cars do drive fast and enthusiastically from time to time but do so in a responsible manner and typically respectfully go with the flow, whereas a lot of people with more regular cars (mostly MPVs around here) have a habit of driving a good deal too close and a good deal too fast every single day. Many even engage in some truly reckless behaviour as soon as they feel threatened/frustrated, a telltale sign of power/control issues.
Your point about people seeking to drive faster is a valid one.
The counterpoint is there are people who cannot afford luxury cars but also want to drive faster -- they'll end up buying cheaper cars that can drive fast within their price range. Those are likely to be more fatal than the average luxury car.
1) Hypothesis on car age. An accident on a 2002 non-luxury car model is supposedly more likely to be fatal than an accident with your average new car.
This matters because Teslas with autopilot are relatively new compared to overall car population.
2) Hypothesis that low cost cars are more fatal than an average luxury cars.
3) Demographic hypothesis. Because of price point, the buyer demographic of newer luxury cars will be different than the overall demographic. Age group (e.g. teenagers vs. young adults vs. older adults), education level, profession.
http://www.cbsnews.com/news/report-lists-cars-with-highest-a...
The fatality rates are probably also notably better on late model cars relative to clunkers because of safety features.
I don't think more expensive cars are less likely to have that kind of accident, nor would it be less fatal.