I'm not even quite sure it's entirely possible, to be brutally honest.
But maybe the fact that they're still one of the top exchanges in terms of volume means that their own personal btc price is held in high regards by market traders.
It's almost like the mt. gox debacle...everyone was referencing their prices as one of the top exchanges, which never made sense because they were either artificially much higher or much lower than the rest (which screams manipulation).
Certainly not.
The market works both on global and local incentives. Let me take a couple of examples:
1. If an exchange has high entry and exit fees but low trading fees. There is an incentive, once you're in, to stay in and do your trading there. If the price moves on other platforms, arbitrage
should happen, unless the arbitrage itself costs more in entry and exit fees than the amount of profit it can generate. That's called
spread.
2. If people on an exchange lose faith in it, for example because it takes a long time to handle withdrawals, then people will tend to sell their bitcoins on that exchange and try to cash out. That would drive the price down locally, without affecting the global price. That's actually what happened with Mt. Gox, and many people not understanding this phenomenon actually went there in the hope of buying cheap bitcoins -which they did- only to find out they could not withdraw them.