Lots of people. Good waitstaff and barstaff make good money in tips.
Then you add on the fact that not only are they taxed on the $2.13 an hour (I was paid $2.33 my last waitress job) they are also taxed on their "sales." The last I knew the IRS considered that most wait staff would make 8% in tips on total sales and thus their weekly paychecks not only reflect the tax with held on the hourly wage, but also on 8% of their "sales."
Just in case you’re curious, the IRS doesn’t always tax you based on sales. What they do, is that they have a certain percent that they know is customary for the industry, say most tipped employees get %8 (to use your figure) of their total sales, in tips. So they know people don’t pay on the cash, all the time. So what they do is if you’re reporting below that 8% average, they charge you on top, to stop the people who are hiding the cash tips. Not saying it’s right, or that you were, but that’s the reason why. It’s not meant to be an “extra” tax (on top of what you pay), but an alternative minimum, per se, way to catch the skaters.