Why should you say thank you to someone that serve you.?
I'm think we all should thanks them for their services whether they got money or not for pure humanity and empathy with the other. Think about that: they leave their homes, their families and children, for a whole day (including after midnight depending on the service) to ride around cities delivering things to strangers. They miss their families, they expose themselves to real danger later on streets (risking being robbed or even killed) JUST to deliver your order. Once you close your door, you'll be at your cozy home with a great food while they'll be making the whole way back again. I think all we can do is to say thank you for their service. There shouldn't be a discussion about whether or not we should say thank you to someone else. That's an absurd.
A "thank you" costs you nothing yet means a lot to the person you say it to. There's no reason to withhold gratitude unless the server did something wrong. Most of them earn very little.
If they have done their job and you are satisfied with their service, of-course you thank them. It would be rude not to.
It's simple good manners to acknowledge their efforts on your behalf with a 'thank you'.
Oh for pete's sake, what does it gain you to NOT let service people know that you appreciate them doing a good job? First, everyone likes to have their good work noticed and appreciated. Second, it makes us better people to notice and appreciate the efforts of others. Your "Darned if I'm going to notice or appreciate what others do" attitude is bad for those around you and bad for YOU.
This comes down to personal choice, rather than there being one right way to speak to someone who works in a service-based industry. Service people are perceived differently, so someone like your friend, will not express gratitude because he expects them to do what they do without any regard as to how they provide the service. Others, like you, will appreciate the work done/the effort made. You can extend this debate out to any profession. Example: do you thank the school teacher or the plumber or the postal delivery man for teaching your child or fixing your toilet or delivering your mail? Perhaps, theoretically no, because they are doing their job but personally, you simply may want to say 'thank you' for what you do, no matter what service is being offered. Whether this be someone in Starbucks or the man collecting your trash, both are offering a service. The level of this service is subjective and so thanks may or may not be expressed.
Thank you mentions are not a zero sum game. They cost you nothing, and may bring pleasure to the thanked. Thanks are the lubricant in doer/receiver transactions. I thank my mail person (and give him homemade cookies), customer service reps and virtually anyone who makes my life easier. Why would anyone not thank another for a service rendered? I would hate to live in your boyfriend's transnational society. Courtesy is cheap.
It happens to be a case for social grace. Blame it on the Bourgeoisie. Restaurants are a social occasion, therefore politeness. Of course, the practice of snarling at the servants was not unknown either. But it is so hard to keep good help!
Because respect given is respect earned. The server is a human being, not a robot. Money exchanged has nothing to do with it. It is the prevailing social paradigm to say please and thank you to people. Like it or not it is just the way it is. A person who fails to follow social protocol comes across to others as less trustworthy and less deserving of respect. It is also poor form because we do not exist in a bubble. The person who today is our server may someday be our boss, or the close relative of a romantic interest, or any number of other situations that could cause bad blood if the person were to remember being disrespected- and it is likely the server WOULD remember. People have a tendency to remember the remarkably negative and the remarkably positive experiences in life, and having someone be rude to you tends to be remembered.