I once worked a buffet as a waitress (not in WDW) and I'm sure I did just as much work as I did in a sit-down place. Many people have the impression that the only thing a server does is bring you food and since you get your own food you don't need to tip much or at all. The truth in many buffet situations is that although the server isn't brining you the food, they are making sure that the plates and utensils on the bar are available, cleaning the buffet areas so that you can get to your food, restocking certain food items that the chefs aren't making on the spot and acting a busboy and server. Buffet was just about the worst serving job I ever had and I would never do it again, the tips in general are the much lower than average and we still made the lower hourly rate.
That said, servers in Disney certainly make their money. I also worked as a waitress in an upscale Washington DC restaurant and made more then than I do now as a teacher, I also was extremely tired, overworked, had no health insurance, no retirement plan, no vacation benefits. I think I single handedly kept a podiatrist and a dry cleaner (we wore white shirts that had to be pressed and heavy starched as a uniform, the restaurant did not contribute) in business. Not all people are as great as the people on this board when it comes to tipping, there are plenty of cheapskates and people who treat you like you are not worth a polite word, that you are lower than them. The number of people who snap their fingers at you, clap at you, or otherwise you hand signals to send you on your way or get you to do something more quickly is appalling. Despite the money, I'll never do it again!