Tipping: Why cabbies and not pilots?

After an abnormally cheerful take-off announcement and a smooth landing on an early morning flight from Knoxville to Chicago, I couldn’t help but wonder: why do we tip certain professions and not others? Why hairdressers and not auto mechanics? Why appliance delivery and not UPS? Why tour guides, bellhops, valet parking, bathroom attendants, and not grocery baggers, librarians, bank tellers, or movie store clerks? Why taxi drivers and waiters but not pilots and flight attendants? [Read the rest here]