One thing I have noticed between travels to Europe and talking to my European friends is that they do tend to go a lot more time for "holiday" and actually take it. Most Americans I know are lucky to get 10 working days a year and half of them don't take it or sell it to their company.
That said millions of Americans travel abroad, they just fly everywhere and are in more of hurry.
Americans also seem to me to be a lot less comfortable in foreign language countries that Europeans. If each of our 50 states spoke a different language it might be different.
What gets me most is the preconceptions most Europeans seem to have of America, and the lack of interest in getting out into small town America to see what the real America is like.
People who avoid the big cities and tourist traps in places like Mexico, and judge those countries by the out of the way small villages and small farming and fishing towns when they get to the U.S. seem to turn around and judge the U.S. by the large cities, tourist traps and interstates and never take time to see the "fly over" country. You can almost cross the entire U.S. without a paved road if you want, and there are thousands of awesome little towns and great simple friendly people from coast to coast.