It used to be that way, too. However, now that the world economy is interconnected as never before, especially world finance, it is all the more true.
The reason there is so much distress in the market now is no one has a clue how bad the overleveraged securitized toxic debt is going to be when it unwinds. This is why the Fed in both Europe and the USA are flooding the banks with liquidity to help them ride this mess out. Most of the toxic debt resets in April, 2008, so we are in the beginning stages of the unwinding. Thanks to hedge funds who are major players in the global economy, there is no safe place to hide because they will be forced to liquidate their good stuff to cover their losses.
so
Interconnectivity is wonderful for the global economy and information flow, but it also sets up the domino effect when things start collapsing. The market hates this type of unpredictable risk and will continue to flounder until it is has unwound and they know who the losers and winners are and which way to go. The foreign money men (China, Saudi, etc.) are already bailing our guys out to keep this from happening, so they are well aware that the US economy could suck everyone down with it if this unfolds in a worse case scenario.
This particular reset is going to be very unpredictable ... so get your popcorn ready.