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For a nation that aspires to be a global superpower, its citizens are not traveling abroad as much as self-respecting citizens of a superpower would!
It appears that only about 20 percent of Americans own a passport. Here's an interesting
web page with some figures.
I don't have the figures for other countries but the American percentage seems quite low in comparison to what I'd expect from most other western democracies - or even Japan. (Canadians seem to have passports in double that figure.)
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There are reasons for the average American's lack of passport stamps. The US is blessed with nearly every type of topography and climate within its borders you could imagine. Intl travel is not necessary if an American wishes to lay on a beach in the tropics, hike in an alpine meadow, mountain bike in the desert or visit a glacier. As for foreign culture, the food and customs of almost every ethnic group on earth can be found here. Most Europeans (N. Europeans esp) Canadians and Japanese need to travel internationally to find warm winter weather. Japanese society is incredibly homogenous, so they have to travel to experience different culture.
As previously stated, Americans also work longer hours in general and have less vacation time for long summer holidays. If you have a week or two only to play with, you're likely not going to want to waste 2-3 days of your vacation just to get to and from your destination. Many also use vacation time to visit rarely-seen family (which may live 1500 miles away, not usually a problem for the Dutch).
This is not meant to deny the parochial nature of many Americans. Many of us have a smug attitude that our way of life is best and see no reason to travel when the best of everything is right here. I for one have been to 4 continents and would like to someday be able to say I stood on all 7. But I'm fairly unique amongst my friends and acquaintances. To many Americans Hawaii and (for the real adventurous) perhaps the UK or France are about as exotic as it will ever get.