The difference between the AFI example you cite and the .mu is that this board gets a LOT more traffic, and so a LOT more people are going to be citing a LOT more opinions, and when message boards reach a certain size, they tend to transition from a circle jerk to whinge central.
I've seen it before, over at LucasForums. Star Wars: Knights of the Old Republic was released, and it resulted in a lot more traffic for the LucasArts message board, but by the time of the third 'installment' of said series (an MMO ), a slough of other successful games had been released, the atmosphere started shifting from positive to negative, as the gaming company became harder and harder pressed to top their best titles.
Same case here at the .mu. Muse are steadily growing in popularity, and with a steady increase of traffic on the boards, there's going to be more and more negative discussion (as their recent methods for getting their music 'out there' are subject to scrutiny as well, dear Twilight). Humans tend to be cynical people, and so it's easy to see the negativity overshadow the positivity.
Did not expect that to be that long.