Maybe we do and we just are misunderstanding each other. I'll clarify:
If a waiter/waitress gives you acceptable service, I feel you should leave at least a 15%-20% tip. If they give you substandard service, you give them a smaller tip. If they completely blow, give them nothing. If the absolutely kick ass, give them more.
All I'm saying is the entire dining out experience is a luxury. If you can't afford (or are just unwilling to) pay the basic minimums listed above, you have, in my opinion, no business dining out. Go buy food, cook it and eat it, no waitstaff needed, money stays in your pocket and you don't fuck someone over who is counting on that tip to make a living.
Tips are the price of dining out. If you can't live with that, you shouldn't dine out.
That's what I was trying to say, and it sounds like you tip when you dine out, so I think it's simply a misunderstaning. Am I correct?