Total trade ... was ~179 kBTC. ...China's slice ... is 90%.
Given the isolated nature of the on-shore RMB market, I would be inclined to simply drop it from volume numbers. If you could measure the fiat in-/out- flows, it would be informative, at least as a measure of sentiment in China, but what actual informative value does a costless swap between traders in a captive arena convey? Call me unimaginative in this case, if you will, but I see none.
The markets are closed in RMB for common mortals, but some people may have channels, e.g. people who run import/export firms.
In any case, since bitcoins can move freely in and out, arbitrage between Chinese and non-Chinese exchanges is possible even if there is no USD/RMB exchange (I gave a simplistic example some time ago). Which explains why the price is essentially the same in all exchanges in the world, with changes propagating almost instantaneously. Contrast that with the last days of MtGOX, when that market was really isolated, in BTC as well as in dollars.
While the raw percentage above may not mean much, volume in China appears to be correlated with volatility everywhere. The lull during the Chinese New Year week is one evidence of that, and one can see on the Western exchanges the effect of the Chinese traders going to bed around 18:00 UTC. Therefore, the fact that the percentage rose from 60% to 90% after MtGOX's collapse is quite significant IMHO.
Higher volume, for whatever cause, seems to make the price more stable on smaller time scales (cehck the 1-minute charts). It may also mean more liquidity, and this presumably means more weight when dfining the price (like a rotweiler and a poodle on the same leash: the poodle may sometimes lead, but most of the time it will have to go where the other wants to go).
There may be a lot of off-exchange trade, but how do those traders fix the price, if not by the open market? The BIT fund, AFAIK, computes the nominal value of its shares daily from the BTC/USD price at various exchanges.
EDIT: typos