Also there is a lot of pump and dump going on, since anybody with 50-100k$ can seriously impact prices.
For example the orderbook of Darkcoin on Cryptsy and Bitfinex at the moment is basically dominated by one guy. He takes his orders off and the whole market gets really fucking fair, really fucking quickly.
If he really wanted to buy such huge amounts of Darkcoin, he would have split his order up, buying small amounts here and there and not just put in one absurdly big order for everyone to see.