I suspect the generic answer is "sentiment" after Moody's put the UK of negative outlook, there is a suspicion that the "read across" will mean the same for the USA, given that both are heavily tied to the markets, in NY & London, massive consumer debts, and a bust housing boom, all supported by massive government borrowing.

Foreign demand for bonds is still fairly solid. But from what I've seen the demographic is changing. China are switching from T-Bills to bonds, etc.

I'd certainly do lots of research on this if I were you, I don't pay much attention to the currency markets, and they're a rule to themselves, so my hunches may be well wide of the mark.

As for the recovery, it'll be a long while coming, the reasons for this is the massive debt overhang, rising unemployment, and a housing market which has a way to go yet until it gets near bottom. What we've seen so far is "stabilisation" things have stopped getting worse at such a frightening rate, but were years away from real economic recovery IMO.