That isn't entirely true.
The crash happened because it is quick to transfer bitcoin, but slow to transfer fiat currencies.

You can assume 2-4 days to get money in to an exchange, rarely would it ever take less.
And so mtgox goes down, people move to other exchanges to sell and buy. The people trying to sell get in first, and eat up the lions share of fiat very quickly. This of course pushes the price down. Much of the drive to drop is by people who just need to move bitcoins out, not really as interested in the price and their main exchange being down. Such as a business who is recieving bitcoins and exchanges them for USD as soon as possible to lock in the current price they are selling at. (and with the price dropping rapidly... the faster you sell it, the more secure that price is)

Then as we saw, a few days after the crash, fiat began to pump back in to the system and the crash stabilized.

Lesson Learned? Keep currency on multiple exchanges. Don't put all your damned eggs in one basket.