Once you start crossing borders, 'nations' become less worrisome. I'd like to know how many of the 'willing expats' have travelled out-of-nation prior to the survey. I'd bet that the majority have. I'd assume that there are fewer of the Americans surveyed who have travelled abroad, but this is just my gut feel. I've heard 'stories' mind you, of people who've never left their counties *shudder*.
Once you leave and explore the world a little, you'll find that many places are quite nice to visit / live for a while. Some will be learning experiences, some will just be for material gain, and others will receive opportunities that their own country can't offer. Why the specific people thought what they did was another topic.
Although one big reason is that there's still the prevailing belief that moving to America will increase your chance at happiness, security, or financial success. I'd still consider that debatable, but the circumstances are very relevant.
http://www.nationmaster.com/co...
Tells me there's a large shift in immigration for people moving into OIL rich nations which makes sense since there's probably a great financial incentive to move (10 year old data alas). The US is 30th, so still pretty strong on the immigration front, but seems to be slowwing per capita over time, which may indicate tighter immigration policies or less incentive from 2005-2008. Of course post-housing meltdown numbers would be more interesting, but oh well.