Tipping is essential. It's the most common generosity exercise in everyday life. It gives us a chance to flex a muscle we don't flex often enough. We should be doing it more, not less. We should tip the cashier at the grocery store and our mechanics and our mail carriers and the referees at high school sporting events. Paypal tip jars and Humble Bundle's Pay What You Want model are two examples of tipping on the web…
Don't forget your software development consultant. I wouldn't mind an extra 20% :) I'm not convinced of your point, but I wonder how far you could take it. Do you tip your kid's teacher, your professor, a librarian, your doctor, your doctor's assistant? What if the referee is actually wealthy and does it for the love of the game? You'd have to make explicit judgements about every job's place in the socioeconomic hier…
I'm not saying people should tip because they get good service, or because the service provider is poor or because they want to encourage specific results, either in the present or in the future. I'm saying people should tip, full stop.
I am also in no way suggesting that people should be forced, coerced, or otherwise compelled to tip. That's definitely not generosity.
Generosity is good. Sometimes goodness can be goodness regardless of the result. I could care less if it makes a waiter work harder or makes them entitled. That's an entirely different and mostly unrelated problem to getting people to be more generous.