Though only among the rich (about 2.4k in number in 2013) for now, due to tax reason, the rising emigration to Singapore, Hong Kong & Switzerland is a troubling thought, both for the States as well as the countries they move to, in causing economic chaos. Everyone for himself, how can it be good in any country?
But to say that this is "missing friends and family", it certainly does not effect me, whose friends and family are in another country. As for the Americans who are moving out, I'm sure they have been prepared to adapt. My first return to Asia convinced me of this.
Ultimately, it is how much do the Americans/British care about keeping their citizens, instead of finding scorn for those who left.