I am not convinced by that math at all.Silly of them to expect it but there are entire groups in our society who would never think of tipping regardless of income levels
I mean fuck common sense
If I spent a million dollars in my life and do not tip 20% that means an extra $200,000 to spend
You can act all outraged but at end of the day I do better than you do
Maybe if you tipped 20% you would feel like a mensch when waiters would smile at you and it would give you incentive to make 50% more money in your life. And you would be able to have a dinner out with a woman and not get dirty looks from the stuff. Women sure as hell notice when waiters appreciate the tips. Tipping well is actually is a pretty cheap way to score big points with a woman.
Generally being frugal when you MAKE money is reasonable and fine but being frugal when you SPEND money is usually just plain cheap. A smile of a waitress is a part of dining experience. You can cheap out on it, sure. Some people get food from food banks even though they can afford buying it. Others get food from the garbage behind restaurants. There are many ways to be frugal with your dining experience.