Ooh oooh! I know I know!

You are thinking the gold is not like the paper. I agree, we could melt down that gold to make circuitry, gold is a great conductor. The best. Two of these things are insulators, one is not!

The gold coin has value based on its usefulness, but also the two pieces of paper do. I could use the monopoly money to win a game of monopoly, or the fiat to buy food. The gold has value also because it is rare. The paper is not rare.