Bitcoins: Too valuable to accept anything else as payment.
Seriously, it's merchants who decide what to accept as payment. I'd buy steaks with my dirty socks if I could.
This was my original thought when pondering the question.
If it's too valuable for the consumer to spend then it's too valuable for the vendor not to accept.
You don't get this with gold because - although it has an equivalent value to the thing you're buying - it's physically impractical for the vendor to accept. For this reason, Gold is (now) a poor choice for barter and trade but an excellent store of value - hence the hoarding. That's not true of bitcoin.
If widget is worth 1 USD, 15 BTC and 1/1500 oz of Gold then the only thing that effects your choice of which to pay with is which one is more practical. USD has the upper hand in that respect and that's still true today and that's why we hoard bitcoin. Hopefully, it won't be true in the future.
JoelKatz is correct.
BubbleBoy is incorrect.