Hi Osmo, the answer is explained really well in another thread which i cannot find. Basically it is because the GOLD tracking stock is priced in Australian dollars...which are worth less to the greenback by about .1164 ish since the 16th of July or so.
Every unit of GOLD represents exactly .098 troy oz of gold. Its meant to act in the same way as a direct gold investment. There's no hedging and there's a .4% per annum management fee.