If the slimes and UPI are running with it, then they put themselves at legal risk, not to mention they run the risk of getting CBS'd over a fake memo. You can bet your posterior that they covered theirs six ways to Sunday. They have seen the real report or gotten the arresting officer to confirm it off the record. No way they ran with it if they weren't pretty sure.
All of the other news outlets reported what Dan Rather and CBS were saying about the President's National Guard Service and yet only CBS took the heat for it.
If all they say is 'TMZ is reporting a story', then they can slime (if this isn't true) Gibson all day long with no risk to themselves.
It's a noted ploy of the unscrupulous.