Dude, do you understand anything about real life economics? The government creates money out of nothing, not wealth.
LigH is right though. Supply and demand. It's not realistic that the NPCs continuously demand such big quantities of gold stock. As the supply is so big, the prices should drop. You're wrong about the money too. Currently when you buy something from an NPC he gets x amount of trias. This money doesn't disappear because you get it back when you sell something to the same NPC. Of course more stuff is sold to the NPC than bought from them, this means that realistically there should be deflation. The amount of trias lowers so you should be able to buy more with a tria. This doesn't happen either, though.
In short, Planeshift has no proper economy to speak of. Deal with it.