It would seem, as someone said above, that Americans have more of a 'tipping culture' than we do in the UK. (around here, tipping is more to do with old mattresses in quarries) It is indeed bad manners to refuse a gratuity though, and can be seen as an insult by some tippers. As a 'tippee' though, I really don't mind being patronised as long as they're paying.. Sometimes good manners are more important than principles :)