Shouldn't matter if it's on an exchange or not. If someone can buy 2% of the worlds gold on the cheap one or more of three things will happen:

1) Buyer decides to make a quick profit and starts selling on exchanges - driving prices down.
2) Buyer doesn't have to buy 2% of the market on exchanges and demand falls - driving prices down.
3) Buyer just sits on the newly acquired "gold" - nothing changes (for now!).

Am I incorrect?