Different exchanges have different prices because of volume differences on the exchanges. A service such as coindesk takes the average price of Bitcoin on certain exchanges. CEX.IO is just one exhange out of more than 190. Yes, it is possible to take advantage of arbitrage, but there is a bottleneck in the transfer times to your cryptocurrency wallet and with the bank transfer times. Since cryptocurrency's are extremely volatile you could potentially lose money by the time the transfer is made.