I've never understood the present thing, its one thing if it's wine or something else to enjoy together as part of your enjoyment of the punt, but anything else? They're a service provider, I've had cause to see a physiotherapist a bit recently, 4/5 times, she's really nice we have a quick chat at beginning and end 'how are you' type stuff and I pay the bill as I leave, I wouldn't take a fondue set as a present.
On the other hand, teachers get presents from children at the end of the year/xmas, my parents always gave the milkmen/dustmen a few beers/chocs at Christmas and I've been known to tip in a Restaurant - so maybe its just horses for courses