You're wrong. Look at the comments below - you're reacting emotionally and not doing your research properly. I apologize if I'm mistaken, but I'm guessing you're Chinese. I've seen a lot of Chinese people get defensive over little things like this and respond with knee-jerk attacks, but it's really unnecessary. As your country gains influence worldwide you'll only see more articles like this - best get used to it and try to respond in a more useful way.
From where did you get $20 trillion? The data I see show $3.5 trillion for the United States versus $5.4 trillion for China [1]. U.S. depository institutions hold over $9 trillion in savings [2]; this doesn't count savings held in stocks and bonds, the majority of Americans' savings.
In any case, private savings aren't really relevant to a country's credit rating. Ability and willingness to pay are. If the U.S. Treasury defaults, one can sue. If China defaults...you're just screwed.
The Sydney Morning Herald article you cite [1] measures “deposits”. The comparable figure in the United States is $12 trillion [2]. The comparison is misleading, however, since few U.S. institutions, financial or non-financial, “save” in deposit accounts. (This is true in a China, too.) All this comes down to the murky definition of “savings,” which are in the end largely irrelevant to national credit concerns since “credit” is trying to quality their probability of seizure (through default, expropriation or other means).