The thing is, that metals as a form of value for trading has existed for much longer than fiat paper.
Ofcourse we can't keep using physical metals in our age... I don't know how much gold one mobile case bought from ebay is but it'd probably cost more to transfer a tiny amount of gold to china than bringing in the case from there!
But Blockchain should be the next step that bridges the best of both worlds (the fairness of physical metals and the comfort of fiat transactions).
It doesn't have to be Bitcoin, just any well organized blockchain with fairness in mind would be great.