people just can't get out fast enough without being exposed to counterparty/exchange risk of them holding your fiat.
Executing the transaction (at an agreed upon price) and actually getting the settlement (proceeds delivered to you, you deliver the coins) are two separate components.
The convenience of using an exchange like Mt. Gox is that these two essentially can occur at the same time. I sell and then on-demand I can withdraw (as a bank wire or whatever).
If you can trust your trading counterparty(ies) then you have a much easier time finding buyers. Most bulk sellers will allow a rate to be locked in but only if payment (e.g., bank wire) clears within a specific (and short) period of time, but even then they require a premium to be paid.
Another approach is to sell a futures contract on ICBIT.se. For instance, at this moment the spot market rate at Mt. Gox is 44 but the April 15th 2013 futures contract on ICBIT.se can be sold at 47. So that would be an agreement to take a selling price of 47 today but you'ld need to wait for settlement on April 15th. Well, technically you are paid (or charged) variation margin daily with the contract settlement on April 15th. But the point is that you can use futures contracts to lock in a price.
The problem with that approach is that there aren't 10,000 BTC of liquidity there. But they are growing and someday that type of transaction could work.
Also, along the same lines you could write CALL contracts on MPOE (at MPEX) at a certain strike price (or buy PUT contracts). There they do apparently offer liquidity for that size of transaction. That comes at a cost however as the bid/ask spread is relatively very wide.
Other methods the provide liquidity are coming. CoinSetter and Kraken are two such services that are expected to be launching soon.