i know here in Cali, waiters are required to get at least minimum wage so with normal pay plus whatever they get in tips i'd assume they end up doing ok for themselves.
the whole tipping situation is a 2 way street though imo.
you can use the whole, they should find a better job, or they shouldn't rely on tips arguement and while there's a point to that, you know beforehand that it's an unwritten rule that tipping is expected for decent service in a sit down restaruant.
a tip isn't required although its considered a custom and a norm when the service is decent or better.
if you tip then great, if you don't tip decent service then 9 out of 10 times your usually the same type of person that won't pitch in on bud but expect everyone else to smoke you out, or will go over to a friends get together where everyone else brought food or drink and not bring anything or bring some cheap crap or will be the person haggling or nickle and diming when it comes to pitching in on stuff. most of the time that type of friend usually ends up not getting invited to certian places and the rest of the group will know there's certain places they can bring him to, and certian places where his frugal ways will be a bad look for the rest of the group. again you don't have to tip, but that perception of being the cheap friend, usually comes along with the territory.
that said, if you go to a sit down restaurant and don't tip, do you expect above and beyond service and them to go outta their way to be helpful to you, or do you expect basic average at best service.
i know if i worked in a restaurant and if provided good service and didn't get a tip, the next time you came in you'd be getting the bare minimum service required of me, while my attention would be focused on the other tables instead.