one word: POKER
just like in real life, 99% of the gold on the server is pretty much always in the control of about 1% of the servers players..
it just shifts back and forth between them from poker wins/losses and the high end rare market, mostly poker tho..
when some of these guys loose big, hundreds of mil they look for sellers to buy back in and try and win their money back, then when they win big, they become the sellers in alot of cases
in terms of overall gold, the net gold amount on the server should actually be going down day by day as you cannot buy gold from the store anymore and as people purchase things from npcs, dropped/decayed gold, stuff like that