Normally I would have sympathy but if you post on HN then I have trouble taking it seriously that you can’t figure this out. How could it possibly be any more obvious?
I'm sorry but you lost me here. If I stall my BTC's in a wallet on an exchange, they remain BTC's?
Also I have a feeling that you're not getting my point. It is the selling/buying of BTC's for USD at the BTC exchanges that determines the official BTC/USD rate. Sure you can also exchange them for something else (if the exchange lets you), but this will not affect the BTC/USD rate.
So if on an your exchange you're unable to withdraw your BTC's, you can't sell them, which means you're unable to affect the BTC/USD rate: I.E. BTC price will not go down.