> I wonder how the press is so sure that "fears of regulatory crackdown" are the reason for the drop.

You'll notice that this is true of all race-calling journalism.

"The market was down on news that the Fed ..."

"China's announcement caused the market to ..."

"Iron ore prices rose again after production figures from BHP and Rio Tinto showed ..."

They're not performing exact science. They're hitting the daily quota and moving on. Something that makes for a good, plausible story is usually the limit of what you'll get from a journo in a hurry.