most everything else would also have to be to reflect the relative strength of one organisation to another.
http://www.foxbusiness.com/industries/2011/11/29/sp-downgrades-dozens-global-banks/
Given the fact that the relative balance of strength between organisations is unchanged, changing the rating of the US was somewhat pointless. Indeed, US long term rates have declined, indicating that the market has more faith in the US than S&P indicates.