The medical field is one of the few where you feasibly can charge somebody who doesn't show up. Joanne the hairdresser down the street can't do that because she doesn't have all of your info down to your SSN and in fact she doesn't even have a collections department. Joanne's only recourse is to sit there twiddling her thumbs.
(And, BTW, I know several hairdressers who can go well over $200 for a single appointment.)
This might only be common in the medical field, but I've always seen cancellation fees of around 100% of the appointment price.