That's an oversimplification, and really only applies to fiat currency. What I pointed you toward was the gold standard, a representative currency in which the money could be traded any time for a fixed value in gold.
That used to be the case with the dollar, but now it floats. And now it requires a lot more faith than it did as a representative currency.
But the thing is, all of that isn't really that related to this topic about the mortgage crisis and government bailouts.