The same could be said about revealing transfer plans which every journalist tries to do. It's never the same for every club. We get tons of extra positive media coverage because of who we are. We are more interesting than everyone else. Sometimes it manifests itself into stuff we don't want to see in the media.
Anyhow, my point it banning the journalists changes and solves nothing. There's someone at the club or - hopefully not - the team who has no respect to United, Moyes, the players. In a way, the worst thing that can happen now is the mole keeping quiet after this because it'll make it hard finding him, but he'll still be there and can reveal something later in the season, like ahead of a really big match.