Her's my $.02 on the subject. I have worked in a dealership for 27+ years. And while some of the other things others have said are quite true, I have a little added twist to the problem. A lot has to do with the communication between the customer and the Service Advisor. Let me give you an example of a promlem I had several years ago. A young lady with a brand new car comes in complaining her car "stalls" all the time. The service writer hands me a repair order that states "Car stalls all the time". I check for fault codes-none. I then road test the vehicle several miles and it runs perfect. No problem found. She comes in on several more ocassions with the same complaint, and I still can not get the vehicle to stall. I call the tech hotline and they have me replace several parts, including the engine computer. Still she complains of the stalling. By now, of course, everyone is getting upset. So the shop foreman goes for a ride with the customer, and discovers that the vehicle does stall, when the vehicle is coming off the interstate, and the young lady does NOT push the clutch pedal in at the stop sign! The shop foreman asks her why she didn't push the clutch in, and she replies "I didn't think you had to when the car was in 5th gear!" So nothing was wrong with the vehicle in the first place, there was just a comunication problem from customer-service writer-technician. This is an extreme case, but it happens so often, it's not funny. I personnally have always done my best to repair a vehicle when under warranty, to keep the customer happy, and coming back for service. This is not to say all dealerships or techs do this, but just a little different perspective on your question.
ASE Master Technician