Sure, but what happens if China, India and Saudi Arabia on their turn wants to cash their loans ?If the US were to default today, what would (could?) these creditors do about it? Everybody assumes the US will always behave responsibly. Maybe it's time for that worm to turn. ;-)
And yes, I am playing Devil's Advocate... but the fact is there is NOTHING MUCH anybody could do if the US decided to be selfish in this or any other respect. Its detractors might like to think about that.
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1