I don't think it is because of the PMs - the posts are public
and while it doesn't seem very nice, Epicurious does have the right to remove posts from their forums.
I think if they had an issue with private messaging, they would disable the feature for those they feel are abusing it.
Now the editing of posts to remove attributions to other sites and publications - that is a whole different ballgame, particularly when they have no posted rules or guidelines against doing so. In fact, they have in the past, asked and encouraged folks to post attributions and links to sites if they posted recipes from them.