You're right. I don't see you're point. Again, YOU, as the contractor, set your price with Mrs. Evans. You determined what price would cause her to hire you, cover your costs, allow you to profit, and keep you competitive with other painters. Too high, she won't hire you. Too low, she won't trust the quality of your work. It doesn't matter. Painting is not a traditionally tipped position.
Taxi driver? Sure. It just is. Taxi drivers, especially those who lease their cabs, pay so much they earn pretty much NO money from the fares. That's just the way it is. Most of their income is from tips.
McDonald's workers? They earn at least minimum wage. Table service is atypical. Tipping isn't - or shouldn't be - expected. Same for any similarly-designed restaurant.
Table service restaurant, on the other hand: in most states (43-44, I think), servers are legally allowed to be payed a mere $2.13 an hour with the expectation by the government and the employer that tips will at least cover the difference between that and the state's minimum wage.
Other careers on that page I linked? Well, they're service industry careers. You want to tip? Great. You don't want to tip? Okay - keep in mind, the hair stylist controls the physical image you present to the public

, the valet saves you time and energy - you don't need to drive around finding a parking space, then walk long distances between your car and your destination; etc.