I can tell you have never owned a luxury car. I have for several years… and my owners manual specifics regular gas. Why would anyone want to waste their money on premium gas when the car maker says use regular? Unless he thinks he’s smarted than the people that designed the engine. 
I agree that premium is a waste of money if the manual specifies regular. I was talking about people who buy expensive cars with high-performance engines that require premium and then decide to be cheap and run them on regular. I assumed that most cars in the $30,000+ range fall into that category, but apparently not.
And how exactly can you tell I’ve never owned a luxury car? I have a 2003 BMW, and the manual specifies premium.