As a server I gotta say this; even if tips were abolished I’d certainly not give everyone the same service. A nice regular who comes in every week and is friendly is definitely getting better service than the sour middle aged couple who complains about everything. 

Like I get what you mean but it’s not only tips that make service different. I’ve had regulars that tipped heavy but we’re an absolute terror to serve, I did not do anything more for them than basic good solid service. The tip was not enough to cover their entitled terrible attitudes.