You might also wonder how you can pay for purchasing things in China for 0% fees using the Chinese equivalent of PayPal and then further why the sellers are only being charged 1% (at most) for using the same service.
It basically comes down to the population size (well over 3x that of the USA) and the general expectation of low or no fees that the population has (unlike the US population who seem to be resigned to being constantly being ripped of with excessive fees by using services such as PayPal).
There are small percentages charged for the withdrawal of funds to banks by exchanges so the model isn't "fee free" but the lack of any trading fees and the support for "bot trading" guarantees the greatest liquidity possible.
Also as the large exchanges in China are closely tied to mining this liquidity is particularly important for them (so the Chinese exchanges work more like an overall Bitcoin service system than western ones do). In this regard you can even find that one exchange (BTCC) offers the ability for you to "create a permanent message" in the blockchain (just like Satoshi's initial message in the genesis block).