Interesting thread.
There are many urban legends of tipping and why it began. One such legend states that in early America, tavern servers were horrible in their service. Small baskets were placed on tables with the words "To Improve Promptness" written on them. If you wanted your "Waiter" to come to your table and serve you in prompt fashion, you put some coin in the "T.I.P." basket.
Nice story. Perhaps it's true. Whatever the reason, it's a fact of life that restaurant waiters/waitresses in the U.S. expect a tip. Those of us that grew up with this are simply used to it.
I do like my European travels. It's a bit different in some other countries for sure, but I still tip.