Why does it matter? That isn't some kind of gotcha.
I wouldn't mind if 100% of customer facing jobs were tipped. At worst, is an optional lower price to pay if you are dissatisfied or light on cash. Normally it is just I'm part of the price. I'm not sure why people would be so much happier paying 120% the price instead of 100% and then a 20% tip. It's all the same in the end