Another factor is that the markets are paper thin at the moment, and are only just starting to recover from the recession. The dealers are looking for signs in the market for what is going to be happening over the next few months to years, and comments like those do tend to encourage people to bail out..! It gives a signal for increased regulation and control, something the markets have always been skittish about.

You can see it in the money markets as well. Someone at the BoE makes a comment like "if inflation stays high we may have put rates up" (not really a sign of anything, just a quote from the basic book of monetary policy) and suddenly the markets are all over the place, selling off and rallying with no real pattern at all.

Its jumpy dealers who've had two years of crappy markets looking for signs from above about the future. If theres even a whiff of the future being bad, down go all the indices.