Exactly. There's no global police force that comes to foreclose on your country when your debt hits a certain level. What happens is that when people have doubts about your ability to pay your debts on time (relative to other investment options,) you have to pay a higher interest rate.

But in the case of US debt, the opposite seems to be true: http://4.bp.blogspot.com/-iFxt2vNk2y0/TZNxgTINNEI/AAAAAAAAAW...

When Moody's downgraded the US credit rating, the response was a rush to, not a flight from government bonds.