the reason you don't see a difference in service is becuase the waiters are trying to earn a tip. if htey knew you are a cheap bastard, then your service will ****.if you consistently go to the same restaurant and repeatedly screw your waiter, they will soon remember you and then you will see the quality of your service decrease. you'll be sitting there with an empty cup, maybe the wrong order, waiting for the check, etc.
that's why waiters get tipped, to make sure that doesnt' happen.
when i waited tables, there were a few people who always tipped like shit, and we remembered them. i made sure to always take as long as possible on everything for them, as i knew it wasn't going to do me any good to be on point at all, as i would receive the same amount of money no matter what. i let their glasses go dry, i delayed putting in their order, i never bussed their table, i never checked on their food, i basically ignored them. i was hoping they would never come back, so that i wouldn't waste an hour on them not making any money while good paying customers were sitting somewhere else.