How can you possibly argue that tipping 12-15% (20% in New York and higher end places elsewhere) is not the overwhelming norm in the US? At every level of service? Whether you're eating at Nobu or getting your hair cut at Supercuts or just scarfing down a Denny's Grand Slam, those numbers are overwhelmingly accepted as standard by the virtually all Americans. The service providers, on the other hand, accept the pay and in essence agree to serve you on the basis that the customers will adhere to that norm. This practice is so clearly understood and adhered to that it need not be spelled out except occasionally in restaurants catering to an international clientele ("A suggested gratuity of 18% is added to all bills...").

That a small - very small - number of people have the chutzpah to decide these implicit norms of tipping don't apply to them does not make them any less of a boor. While I, just as PaulMSN, have no hard numbers to back up my claims, I think your assertions that "plenty" of people do not follow those norms is wildly off base and simply a way of making freeloaders feel better about saving a few bucks at the expense of someone else. For those who think tipping is in fact optional, try walking into a restaurant and announcing you will not be tipping before being seated. See if you are served (or if you are... avoid eating what you are served). The only reason one can get away with not tipping is because you're in essence lying by omission and implying you will follow the norm. Only after the service has been rendered do you withhold the expected tip.

On topic, OP's bag should have arrived properly. The Skycap should be fired. Lots of people make totally innocent cultural faux paus and the punishment for that should not be having your bags misrouted (or food spit in or whatever). But I have no sympathy whatsoever for OP's plight. He knew the rules, he tried to cheat the system, and his bag ended up in Tahiti. Live and learn.

[Edit to add:] Not dispositive, but many use just landed for orientation in a new country. From the tipping section: "There’s a long tradition of tipping in the US, where greasing palms is both an integral part of the American way of life and a social disease (tippititus), and has nothing whatsoever to do with the quality of service. Americans are prodigious and prolific tippers, which isn’t normally regarded as discretionary. Non-tippers are considered cheap (the ultimate insult to an American) and are treated with contempt, particularly by taxi drivers. Most Americans are shocked by anyone who doesn’t tip or who tips too little... [M]ost Americans would have to receive atrocious service not to tip at all."