"But you can always trade it for any currency anywhere."
Not true, a plainly absurd statement. I'm going to the airport in a couple of days, can I trade gold for a few AUD, or USD? Tell me which company willingly trades gold at the airports for a currency. In addition, how are they going to check the gold purity, they don't have the facilities or the expertise to do it.
Can you go into your local bank with gold bars and trade them for AUD?
If you had said USD can be traded anywhere, the I would have agreed with you. Gold is illiquid, and there's huge commissions.
