In the Midwest of US the hourly wage of a wait staff is $2.38, that is why it is customary to tip wait staff. The tip is 'earned' by their service. Some establishments pay a bit more, maybe 5.00 per hour and you still rely on your tips. Tips are taxed and the waitress must fill out a slip for the employer every week. If you don't fill out the slip the govt. expects that you made at least 10% tip (that was a number of years ago not sure of % today) on each bill and will be taxed accordingly. If you leave no tip they still must declare that you did. If you run out on your bill the waitress must pay the bill herself unless the owner is a nice guy and takes pity.
The wait staff is usually expected to tip the bartender and busboys at the end of the shift from her tips and is entirely up to the waitress. So if a bartender was chatting up a cute guy instead of getting your drink orders ready the bartender could get a lesser tip from the waitress for the night. Kitchen staff (cooks, chef's etc) are not tipped by wait staff because they make higher wages.
I also worked at a private club where no tipping was allowed and the wage was quite good, private members were tools but that's how it goes.
I was a waitress and understand the tipping situation however I do not tip at a sub shop and often not for coffee either because most barista's make about 15.00 per hour and some even get health care. Though I don't really go out for coffee so to tip or not is an afterthought "oh crap was I supposed to tip?" or else I tip too much.
If you watch your waiter/waitress you can see if they are one of the good ones or not. Back in the day I refused to work anywhere there was shared tips. Just made for lazy co-workers while one or two worked their butts off.