They are in business and have to make money. They have a buyer who can afford the price of the car and therefor should be able to afford the service, labor and whatever else they can throw at you and they know people will pay it. Also most people don't know shit when it comes to cars and will gladly pay someone else to do the work.
That said, they will rip you off, I blew a caliper and some pads at a track day and had no supplies on hand to fix the problem and had to take it to a dealer to get back on the road and home, they charged me about $900 for parts and labor on something that I could have gotten the parts (a rebuilt caliper, and pads) for about $200-250 and spent 3 hours or less fixing. Since then I don't goto the track without extra pads/fluid and a couple caliper rebuild kits, and sometimes a spare caliper or two!
I will however take my car to the dealer for a big service or something along those lines because its in such great shape and I would like it to stay that way and now that I have a job I just don't have as much time to tinker as I used to.