Cashing out 100 000 USD however is a different story. It actually happened a few hours ago, you can see the impact for yourself[1].
All demand is not reflected in the order book. In fact, most demand is not. The more sophisticated a trader is, the more likely he is to use limit orders to manipulate the market instead of the rather stupid move of telegraphing demand.
If the market went down 10%, a flood of buy orders is not unlikely to appear.
It works in both directions, people who are speculating on Bitcoin will be easily spooked by a medium-term crash.
midnightsine is pulling his numbers from limit orders posted on MTGox. I'm saying that's not an accurate measure of what it would take to send Bitcoin to 0.