Bitcoins are even cheaper on BTC-E and Bitstamp.
I'll agree that BTC-e tends to be lower, but only slightly -- it's also pretty highly accurate, because you can actually wire into it usually (I have been told) and its support of LTC pairs causes arbitrage to hold it and OKCoin in particular, very much on spot with each other, which has the ripple effect of holding the other Chinese exchanges somewhat at a reasonable level, particularly BTCChina. The arbitrage triangle of BTC, LTC, and CNY with OKCoin and other Chinese exchanges, and the triangle of BTC, LTC, and USD with BTC-e and other USD exchanges. Bitstamp can't float high because of Coinbase. Gox is the anomaly.