What makes you say that gold and platinum are precious metals? The average market works like this: The more abundant a resource is, the less market value it has. Also, the more useful it is for potential buyers, the more market value it has. And vice versa. I don\'t think anyone knows what the market value for these ores are, as we have no clue how the PS economical market is laid out.
However. Let\'s not forget these are raw materials, and not finished products. Therefore they should sell for ridiculously small amounts of money, just like in REAL LIFE. Because manufacturing items from the raw material costs both time and money, the finished item should have a great increase in value.
It\'s all about balance, in real life you dont just go down to the \"magic shop\" and start digging out huge pieces of gold ore. It\'s a lot easier in PS, therefore it should be worth less in PS.