I think the nail was hit on the head when someone said that the forum stopped them from bothering to buy magazines.
The question you have to ask is do some magazine editors feel threatened by forums who they feel might draw away their customer base.
The the Hifi+ article was recent it's not the first time they have made noises about forums and non accountability of posters.
Yet the vast majority of posters have nothing gain from giving advice which they do freely purely from love of their hobby. Even many of posters who are in the trade do the same as well.