It would be if that's what they made every hour and worked 40 hours a week. But, for example, when I was a waitress, the tip I was getting had to be shared with my busboy, the bartender who got my drinks, the hostess, the food runner and the kitchen. Out of that $20 I would get $10. Our tips were not added automatically either, so most of the time I wasn't getting 20%. It ranged quite a bit.
The other factor is that the rush hours are shorter than a normal eight hour shift. Usually there are only a few hours where the sections are full. Even then, most nice restaurants don't seat more than a few tables in a server's section. In my first restaurant we each got three. The next one was five, but the amount I was expected to tip out was higher, so it averaged out to about the same take each night.
Most waitstaff doesn't get a full 40 hours per week. My restaurants kept our scheduled hours below the amount where they would have to provide us insurance. Which of course meant that my tips had to also cover private insurance, which is very expensive here. Not to mention my clothes for work, which almost no restaurant provides for free. So while I would say that I would average around $150 a night, I only got to work 4 nights a week. Now, WDW waitstaff is a much higher level than I was. They probably make a lot more. But it's not the astronomical amount you're thinking, and they probably have more education to do it than you think. And it's a hard job. It's being on your feet the whole time, often getting treated poorly by customers, yelled at by the kitchen, and high stress most of the time because the timing of everything has to be perfect. It's not rocket science, but it does deserve more than minimum wage.
I have seen threads closed when the discussion of whether or not to tip has gotten too heated, and I would hate to see this thread meet that fate.
