Which means you can buy and sell to yourself at no cost.
This happens on "our" markets as well (the buying and selling to oneself) but fees make this prohibitive. On those specific exchange you are referring to, there are no disencentive to manipulate prices that way, hence the probability that a big % of this volume is "washed" as we say.
This is why such volumes are not taken into account.
i wonder if no fee exchange will become popular for btc/usd in the future
If the Chinese exchanges charge 0.01% fee, the trading cost will make the volume drop 90%.
0% trading fee makes a huge difference there. The market can be manipulated at little cost.