The difference is, their economy could collapse. However, U.S. economy collapsing is 10x more probably due to the insane debt they've built. As an example:
According to an article in MSNBC news updated April 6, 2008, the U.S. owes China 492 billion dollars.
Wow.. how come a mighty power such as U.S. get money from a poor country like China? 
Your argument holds no water. A number of the countries ahead of China on the IQ list are not as technologically advanced or a number of other things compared to the USA. Yet, you think China, for whatever reason, is going to be the only country to do it, when they have a multitude of problems brewing down the road for them. You're just assuming, and you know what happens when you assume.
They'll never collect on the debts. We won't pay and they need our trade relations.
