I don't usually go for the whole "conspiracy theory" thing, but Billmon provides us with a link to a story at Buzzflash entitled "Will the 2004 Election Be Called Off? Why Three Out of Four Experts Predict a Terrorist Attack by November."
While the Letterman episode is a lesson in abject absurdity, nearly two years ago, Madsen and Stanton warned that following a major terrorist attack, seditious web sites would be blocked (something that is already happening to howardstern.com) and "the broadcast media would similarly be required to air only that which has been approved by government censors." (How will we know the difference?)
Read the whole thing. I'll send a chill down your spine. I'm not so sure about the theories, but it's always fun to play what-ifs.