Most of the people(mods and such) on those sites are either people that are trying to sell their products or are diehard fans that swear by said company solely because it's what they like the most(says nothing of their progress with it).
There are a few honest people on company boards, but they definitely aren't too common.
Which is the main reason I love AM. These guys(for the most part) have no ties(and keep honest logs) to companies.
Lastly, supplements are only supplements. If one guy is putting 40% into his workout/diet with the product, he's gonna get very little/nothing out of it. If another guy is putting 110% into his workout/diet, he's going to progress a lot farther(and usually give credit to said product).