+1 most waiters don't even get paid minimum wage. And a portion of their tips are split between other staff also (i.e. bussers, bartenders, hosts etc.).
First of all, this isn't always the case. Secondly, my tipping has nothing to do with my waiters income. I don't care if he's Bill Gates, or a homeless dude. If the service is worth tipping, I tip(well) otherwise, he can starve with his children, and think about how to be a better waiter next time. I hate this preconceived notion (which may not have been your point) that if the service isn't good, and it's the chefs fault, or someone else's fault, you still tip the waiter. The tip is at your discretion, not to be added automatically. I've had places add a tip to my total, when the food, and the service were an utter disgrace. I simply deducted the tip and left cash.