Joan Walsh explains the mainstream media's reaction to Stephen Colbert's speech at the White House Correspondents Dinner in this Salon article:

"Colbert's deadly performance did more than reveal, with devastating clarity, how Bush's well-oiled myth machine works. It exposed the mainstream press' pathetic collusion with an administration that has treated it -- and the truth -- with contempt from the moment it took office. Intimidated, coddled, fearful of violating propriety, the press corps that for years dutifully repeated Bush talking points was stunned and horrified when someone dared to reveal that the media emperor had no clothes. Colbert refused to play his dutiful, toothless part in the White House correspondents dinner -- an incestuous, backslapping ritual that should be retired. For that, he had to be marginalized. Voilà: "He wasn't funny."