Well, for one, the market traded gold is not real gold. Try to buy some real physical gold for the Comex price - it won't happen. Even if you buy a ton or so.
The thing is, gold is more than just a asset like any other. Gold is also a mirror of the value of the fiat currencies, its a instrument of power plays between rivaling countries, and its a fear indicator in a economy. Silver is similar, by the way, only its more for the small people. And the practical use in the industry has a bigger role like in gold.
Over all, the price for gold - real gold - says more about the currency that is used to buy it rather than the "value of gold". The value of gold is basically always the same: 1 oz of gold is worth 1 oz of gold. How many US$ or Euros or whatever you get for it, that's the variable part in the calculation.