So how many hours is the walking waiter working in a day, and how many hours is the standing waiter working?

If anything it seems to me that it would be more logical to tip the person doing the more boring and repetitive work.

(My personal opinion is that tipping in general is a blight on a modern society and something that belong in primitive third-world economies. The way to fix this is via legislation: we simply make all forms of both receiving and giving tips illegal. It probably won't take much enforcement to quickly shift the social norms and economic practices once the wheels get rolling).