Comparative passport ownership
Many are the articles, such as this one, that decry low levels of passport ownership among Americans as symptomatic of an insular mindset. I think a more likely cause is the sheer size of the United States--you can't really compare the U.S. to other countries in terms of passport ownership. The other largest countries geographically all have their numbers skewed in some way. They have repressive governments, are very sparsely populated, or or just too poor to support much international travel.
As a result, the United States is compared to far, far smaller political entities which do not share our geographic breadth. If the states were separate countries (and most of them are comparable in size to European countries), the United States would have almost universal passport ownership--I don't believe I know anyone who has not traveled to a different state.
So take that Europe. We're not insular; we're just huge and free. I predict that in the Schengen Area levels of passport ownership per capita will begin to fall, but you know that there will be nary an article decrying the insular nature of non-passport bearing Europeans.