In many locations, waiters obtain minimum wage or just above that, so tipping is their means of making an income above that of working at a Walmart. In Florida, it is worse, as waiters get paid somewhere around 1/3rd minimum wage, so tips are really their only income.
Cab drivers as well. The money spent on gas, on rent of the vehicle, and on general expenses while on the road, easily swallow up that base cost for using a cab. Tipping is their bread and butter. Indeed, many cab drivers end the day at a loss and end up having to work twice as many hours as other jobs just to come out with decent income, particularly if nobody tips.
So, tipping, yeah... it's a need associated with the job. You don't want to tip, that's your choice, but it's also not respectful of the efforts some of these peeps make, particularly if they're entertaining or at the very least friendly.
However, if they're asses, why bother tipping? Customer service jobs, those that are dependent on tips, don't need asses and not tipping may help to move them to a job they're more suited for.