Waiters in Europe are not necessarily slow or less knowledgeable, and waiters in the US are not necessarily fast or knowledgeable. What US waiters are, is visibly polite (obsequious, even?) and ever present.
In Europe it's perfectly normal to have a rather rude waiter who takes your order quickly and your food not long after that. They can also be efficient and know the menu in detail, albeit being colder when you discuss with them.
The shock Americans experience is probably due to the frequent stone faces of waiters in Europe.
That's what real people look like when they're not conditioned to always smile and instead they smile when... they feel good :-)
Say no to PanAm smiles :-D
I'm not advocating the US way of doing things, and certainly don't think the service in the US is better on the whole, in fact in many ways it's worse. However what I have found is that the worst service I've had in the US is far better than the worst service I've had in Europe. I've never had terrible service in the US, and I certainly can't say the same about Europe.
Because the whole point of going out to eat instead of cooking at home is to have an enjoyable and stress free experience.
If it takes 20 minutes before someone asks what I want to drink, then 60 minutes to get food, you cannot answer any questions about what is on the menu and half the people get the wrong thing and then that completely ruins what should be an enjoyable experience.