An SL 55 is about $120k. Plenty of non millionaires drive cars that cost half that (and I bet there are non millionaires that drive SL 55s) - for a billionaire, where it's a rounding error on his net worth (though probably not on his liquid cash), it basically is frugal.
Quite. He could afford to have a custom iBentley made if he wanted to. Also I don't know how the SL55 stacks up in this respect but if it's more reliable than average, then that's a frugal choice too. Remember it doesn't mean cheap it means best possible value for money.
I don't usually respond to say I agree with something because it's against hn rules, but that's a really interesting perspective. I didn't think about it that way and it makes a lot of sense.