I remember having a conversation with an American about this very subject, and he mentioned that not that many US citizens had passports. Your post brought this to mind,so I went to Ask.com and put the question, the article below is the first of many links. To read the full article and the many links within it , I will post the web link.
http://gyford.com/phil/writing/2003/...y_american.php
Writing
Friday 31 January 2003
How many Americans own passports?
One of the reasons America is sometimes described as being an insular country is the low ownership or passports, and thus the low rate of international travel. Which in some ways is fair enough; in comparison to Europeans, for example, popping over to another country is often a bigger deal than jumping on a train. But Ted read that only 7 per cent of Americans own passports and wondered where the figure comes from. It seems the statistic varies, for example:
25%: “75% of Americans don’t own a passport”
22%: “just 22% of Americans own a passport”
<20%: “less than 20% of all Americans own a passport”
15%: “85 percent of Americans do not own a passport”
10%: “only 10 percent of US citizens *ever* own a passport”
<10%: “fewer than 10 percent own a passport”
7%: “only seven percent of Americans own a passport”
None of these are remotely official but I can’t find an official government statistic for passport ownership. The closest I’ve found is this page of the number of passports issued per year. First, lets be generous and say that every passport was issued to an adult and therefore lasts ten years. Assuming that everyone who’s been issued a passport over the last ten years still has it, that’s 60,884,784 people with US passports. Given the US population is around 280 million, that gives us 21.7 per cent owning passports. Taking into account some of these will be five year passports, we have a figure that’s probably a little under 20 per cent. Is there any reason this calculation would be way out?
Incidentally, I graphed the statistics for US passports issued per year [updated 24 April 2004]. You can see the dramatic rise over the past ten years. This may account for some of the lower figures people give; they could simply be out of date. Using the same method for the years 1981-90, for example, we get less than 15 per cent ownership, without taking into account five year passports. If the rate of issue stabilised at around 7 million per year, never mind further growth, then by 2013 around a quarter of US citizens will own a passport (assuming the same total population).
Update: From the comments, the Economist has a subscriber-only article that states 34% of Americans over the age of 18 own passports, but cite no source for this. By comparison, it says 41% of Canadians over 18 have passports. (10 Sep 2005)