Me too. Sometimes I feel that a lot of the "thankfulness" that goes on is a little extraneous. I worked at a fast food place for a year in university, and I always felt a little weird when people said thank you after I gave them their order. I didn't do it for them, and I didn't give them any special treatment. I was just performing a task in exchange for money.
I was raised to say thank you when people helped you out in any way. I guess I understand the thank you when you make food for people because to them they are paying for the food, but someone (who is probably underpaid) still had to make it. People that actually appreciate cooks an severs tip, saying thank you is more of a common courtesy/practice. Also, I think a lot of people get that they don't pay the cooks, they are paying the owners of the restaurant so the thank you may be more or less genuine in that situation.