I dont doubt that. But if they are any good at their job they will use these boards for story ideas or to give a sense of different opinions. If they dont follow that up by talking to their own sources, they are not going to do very well in their careers. That is lazy and their articles will be boring and uninformed.
If you are a journalist and you say x, y and z is happening at the club, based on rumour on a message board, and then it turns out you were completely wrong, how many times do you think you can get away with that before editors stop giving you commissions? When people have a reputation in that business, and write for various papers and websites (as listed above, quite reputable ones in Mitten's case) it is probably because they have a track record of writing things that are a) clear and well written and b) right more often than wrong, i.e. well connected.