This must mean that...

Investors around the world reacted to S&P's downgrade of the US credit rating by selling out stocks. They also started buying up a whole bunch of US government bonds (see here how yields on medium to long-term Treasuries were decreasing today). Which makes sense, right? In the time of uncertainty caused by the fact that the US federal government is apparently more likely to default in the medium run than previously thought, it's a good idea to invest in the safest assets around, such as medium-term US government debt.

What, my explanation doesn't make any sense? You tell me then.