Pastor refuses to tip "I give GOD 10% why do you get 18%"

[Rain Man]

The other thing I don't like/get about tipping is that I can go into the following three restaurants and get the same level of service and tip different amounts (assuming 20%):

1. I go into a diner and pay $12 for dinner and leave a $2.40 tip.

2. I go into a midscale restaurant and pay $25 for dinner and leave a $5 tip.

3. I go into an upper-end restaurant and pay $75 for dinner and leave a $15 tip.

Now, in the upper-end restaurant I'll usually have the fellow who fills my water glass frequently, but otherwise I don't usually see much difference in service. Why does the waitress at the midscale restaurant get twice as much tip money when there's no difference in the amount of work they do? It seems unfair that the tip is based on the cost of the food.

And I should point out that I've never received a tip in 20+ year of work as an engineer, economic research, and market/demographic researcher. I really think there should be more tipping in these industries for work well done.