He had me until the dentist story. I don't think that a dentist actually plans to let patients wait, but it does happen. A dentist (mine at least) usually plans in contingency for emergencies, but it may still happen that he overshoots.
Question: Would you rather have your dentist hand out his cell phone # after treating you on a Friday and their may be some complexities on the weekend for the price of waiting the occasional 20 minutes or a guaranteed punctual dentist who lets you wait for three weeks while you agonize in pain?