http://www.nytimes.com/2012/03/11/opinion/sunday/the-go-nowh...
The difference may come down to how we grew up; my father traveled quite a bit when we were younger, so I lived in France from ages 3-6. I thought those few years added to my life experience and gave me a unique cultural perspective. My girlfriend never moved growing up though, and she believes that moving hurts the friendships that young children develop. To be honest, I'm not sure who's right. I was always kind of introverted, so I didn't have particularly strong attachments, but she is very outgoing and extroverted and still keeps in touch with friends from elementary school.
Kids are stuck near their parents because they can't get decent jobs.
If they're still living with their parents in their 20's, well, they can't relocate unless whatever job they have can absorb a huge increase in housing cost.
And, even if they did move out, they're so close to the economic edge that having Mom and Dad nearby when the car breaks down, the washing machine dies, etc. is huge.
Sure, unemployment rate may be different in different areas, but why move from one McJob to another McJob?
50 years ago, if your girlfriend said she didn't want to move but you got a job across the country you would probably both move across the country. In part that's because you would likely be the primary income for the two of you and partly because women's wants were not often considered as equally important as men's wants.
Would that have been true in every case two generations ago? Maybe not. And would it still be true in some cases today? Probably. But the odds have changed over time quite dramatically. My wife earns nearly the same salary that I do (and made waaay more back when I was a student). We can't move somewhere unless we both have job offers lined up.
Also, our culture now has a rather unhealthy (imho) obsession with trying to make life perfect for our children that previous generations were less inclined towards.
The reverse brain drain might not be long term but if that trend continues I dont think the western world has to worry much about jobs being lost.