after the thrill of buying something with a gold-based currency wears off, people rarely use it. Instead they tend to hoard it, keeping it as a store of wealth.
I think this could be said with almost any form of currency that isn't paper or plastic, people will hoard it.
Hell, people hold onto change more than they do their bills, I believe it is subconsciously because it is 'heavier' thus has more value. Or not, whatever, but I believe my joke argument as much as the gold hoarding one, and both theories kind of compliment each other.