Another point most of you do not aware is that Chinese BTC exchanges have the best integration with fiat transfer system. Transferring fiat in and out is the biggest headache for many bitcoin exchanges (see MtGox). In China, however, it is completely painless. Taking btcchina, the biggest exchange as example. Users can transfer fiat from any major Chinese bank to the exchange instantly with zero fee. Therefore, depositing BTC is literally faster than depositing bitcoin.
To withdraw, only 0.5% is deducted and in most cases it will arrive in 24 hours. No daily limit. No AML or KYC. All you need are accounts of any major Chinese bank and Tenpay (the Chinese version of Paypal).
(However, this is China, which means the government policy could change overnight)
Then, it is quite surprising the volume isn't even higher.
Could you imagine if it was that easy to get BTC in American, Europe, etc. what would happen to the volume?
Perhaps the storm is just getting started in China...