Associate
Pretty sure you get paid to do a job. Why would i give you more money than you are being paid just for doing your job. I don't tip my bus driver. I don't tip my postman. Why would i tip a waiter? (unless of course it's a huge group of people ordering a large amount of dishes and drinks and the waiter is being fantastic)
For the record i worked in a pub for 1 month and received one 'tip' in the form of a 'keep the change and buy yourself a pint' type of job. That was in my last night working and is probably why i got it. Never expected tips as i was being paid.
Bus drivers are on set contracts with guaranteed hours and often have unions representing them, the jobs are only usually open to people over the age of 21 due to insurance purposes and pay significantly more than minimum wage, waitressing is a much more hectic job often with much fewer hours, I.e peek service times 6pm - 9pm and done by students or foreign workers who may have no other income, postmen get paid extra money by direct marketing companies to deliver leaflets etc and do often get tipped by customers around Christmas, places like McDonald's and burger king the staff are given a meal allowance per shift.