Why is it that some Americans (using the term to refer to citizens of the USA here) think of Europe as a version of the USA on the other side of the pond?

Do they not realise that whereas the USA is a fairly homogeneous culture across the states that Europe is composed of very distinct countries with very distinct languages and very distinct cultures?

Here is an example: http://www.fluther.com/disc/70592/why-is-it-that-europeans-on-average-work-fewer-hours-than/