I knew a waitress at a Marriott who regularly got a party of 10 plus who stayed at their table for an entire evening ordering drinks and enjoying live music. They typically stayed for 4 to 5 hours! She would get no more than 15 or 20 dollars for her efforts. She was regularly distressed when they'd saunter in. They were very sweet people but lousy tippers. The other waitress I knew there did the same amount of work and was thrilled with the tables, the tables my party generally stayed at. Eventually, we began to ask for the other waitress just because we felt awful for her.
funny how differently people see things, see if I (and I think nearly everyone in the UK) was in that party of 10 I would reason think of all the money we've given the Marriott with all those drinks we have bought - why would I pay more? Of course then I would expect the Marriott to fairly pay the waitress for her 5 hours work, whether she spent 5 hours serving a party of 10 or 5 hours serving 5 couples, it's all work and the job she is paid to do anyway - why pay her more just for doing her job??
In my line of work, some of the jobs I work on are easy, some are hard - I don't expect to be given a tip for completing one of the harder jobs though - it's all part of my job that I am being paid for anyway!!