I think many people have a really skewed view of what doctors in the US typically make. I'm not saying it's a terrible living, but I know quite a few who have significant trouble making ends meet after student loan payments. Most don't complete their training and start actually working as physicians until they're around 30, too, so it's a fairly late start in terms of building equity in a house, developing credit, etc.
Friday night my wife and I were told someone had bought our drinks. I knew I had a patient at the bar, so I guess it must've been she. That's the first time ever that I've gotten a tip, including that one night I worked as a waiter. I have had feces flung at me when someone didn't think I was perky enough after I'd been working for around 50 hours, but that's not much of a tip, really.
We tip instructors in Cozumel. They do not make much, and many only instruct a few hours a week.
Edit: in most of the rest of the world besides the US, physicians don't make a particularly good income. Most do it because it's rewarding in so many other ways.