I actually have a hypothesis that US citizens are actually less likely to even consider going abroad to work because of this filing requirement. There are many other reasons too (the US is a large market in its own right and has been for many years now), but it'd be interesting to compare and contrast the local population count of other developed countries with their expatriate population count.

A follow on hypothesis would be that a country having a larger percentage expatriate population compared to another all other things equal would have more global outlook e.g. the local population is more favorable towards immigration and free trade, and has a more accurate knowledge of the details behind world events.