BAM!  Yes, you've hit the nail on the head.  It is all about liquidity. If we want to see any exchange succeed it'll need to address liquidity on three fronts; performance, bitcoin, and dollars.

On the performance end of things, to allow real time trading, we need something that can handel 1000x more trades per second than either Gox or anything else (other than buttercoin) can handle.  

If a new exchange is going to de-throne Gox, it'll need bitcoins, lots of bitcoins. To do this the new exchange will have to provide solid incentives to potential sellers; top-notch security, anti-fraud measures, low (or no) fees, unconstrained capital withdrawals, fast payment, intuitive interface, and more.  

The exchange will also need dollars, but if the bitcoins are there, the dollars will likely follow.