The question is who will controll all amount of BTC deposited to the exchange?
If its only one person the system would be centralized or I miss anything?
No one controls the exchange system. Lets put it like this: you decide to sell 10 NEU at 0.005 BTC each. 10 NEU are blocked by your wallet, and made unavailable for you until you cancel the sell order. If there is a buyer, he buys the blocked amount (10 NEU), and you receive the 0.05 BTC.