It's not about making anyone dance - it's about rewarding people for exceptional service. Sometimes, when I pay someone to do some kind of service for me, they go out of their way to be better than average. That is just what happens in human-to-human interactions, and I want to honor that. It's the reason to give a bigger tip than normal (now don't tell me you never did that and always tip whatever is your absolute maximum), and it should also be the reason to give more than the average amount of stars.

Oh, and btw: it's the same the other way round. I also sometimes put much more effort than strictly required into my job for a particular client, and I love it when that is recognized and honored. If it is, I am more inclined to do it again later. If not...well, not so much, then it's probably back to "standard service, just enough to fulfill the contract".