As an European (Romanian, more precisely) who has visited the USA, I would say that servers there were much more patient and attentive than servers I'm used to both from my own country, and from various European vacations. I still remember a young waitress who repeated all of the options on the menu literally 5 times going around a table of 15 people.

However, I'm not at all convinced this is as tied to tipping as people claim. My own country has a very clear and old tipping culture (though 10% is the more common "target" tip for food service), and yet service here is often terrible, with bored and annoyed waiters. I think it's much more of a cultural norm than any kind of strong economic incentives.