There was a time when Williams would have gotten away with this because if someone wanted to challenge the story, there would have been no effective means to do so. Letters to newspaper editors or executives in the media would have been ignored. But times, and mass communication, have teamed up to befoul the claims of people like Williams and Hillary.
Williams was in Iraq, so he thought he would add some details to make himself look heroic. At the time, personnel might have been silent because they knew the would have been retaliated against. Now however, that they have retired, they can speak out without fear of repercussions. And due to the mass communications society has, they could expose him without having to go through society's prior filtering system.
Similarly with Katrina, Williams though he would add some details. Unfortunately for him, there were people there who remembered the circumstances, and again, because of the mass communications of the internet, his story unraveled quickly once people began posting about it, and talk radio and FOX began discussing it.
Pretty much anymore, anytime any more liberals claim to have done something heroic, their stories needs to be checked in depth because they just might be lying.
You can always tell when a liberal is lying. Their lips are moving.