Depending on the source it's probably down to ignorance, lazy re-reporting or blind economic ideology, but if you believe that cutting government spending and services during a recession/recovery is a bad idea then it's a scary thing to see.
Well, if everyone believes that downgrade --> stock plunge, or even if a sufficient number of people believe that downgrade --> stock plunge, then it's no surprise that downgrade --> stock plunge.
I think the smart money will be hunting bargains. Pity I don't have any right now.
On the other hand, where else are you gonna put your money?
The long term implication is that we are in the opening stages of the first big crisis that will require significant intervention from China. That's scary for a number of reasons.