Every ten years or so, the U.S. government likes to pop up and try to control what we hear, think, or say. With any luck, it pisses off the population enough to vote an over-zealous, evangelical loon like Bush out of the White House.
The administration hopes that airing the beheadding audio and video will scare the shit out of us enough to keep us at bay, so they can get re-elected.
The best way to control a population is to keep them afraid and to keep them ignorant.
There's a great book called
The Culture of Fear that will really open you up to the scare tactics the government uses to control you.