Just to make things simple, it should be where you were born.
Well,
hang-the-9, you make a great point. Your where-one-was-born view, to me is indeed the way to look at this.
This goes for the MC , Olympics, or any other world-related sporting event.
Let's look at a real-world example.
Remember Toni Kukoc of the Chicago Bulls?
He was born in Croatia and it is safe to say, that when he played in the NBA he lived in the good 'ol U.S.A.
Mr. Kukoc practiced and competed in his sport where he found his work—a contract in this case.
When it came time for the Olympics, he represented, no surprise, Croatia.
And so it should go for a player, say, like Mika Immonen.
He practices and competes in his sport where he feels he can find work.
In this case however, he is an independent contractor; finding his work, traveling to his work, and ensuring for his own logistics.
Heck, he may even be subsidized by someone or some government, but the bottom line is Mr. Immonen is in charge of getting to his work and earning his money.
As we know, Mr. Immonen is from Finland, so when the MC event comes around it only makes sense that he represent his home country.
All that said, I'm against co-opting "foreign" players for the U.S. team just because they decided to visit or even move here.
If you're representing the U.S.A. then you should be born in the U.S.A!
CASE CLOSED.