I don't see how that's relevant to reasons people buy dollars and sell them to other buyers....Facts about the history of dollars may make dollars more stable compared to bitcoins, but what I'm saying is that those facts don't enter into the minds of most people as reasons they buy dollars.
When dollars WERE backed by gold, they easily crossed this acceptance threshold. When the backing was removed, the fiat was sufficiently established. So, while the historical backing is not relevant today, it was relevant to its establishment in people's minds.
There are only 21 million bitcoins out there, so ANYONE could back bitcoins with Gold. If you have 21000oz, you can give out an oz for every 1000 bitcoins.