I think the readers' relationship to a blog goes through phases similar to what we go through in our personal social interactions.
When we first meet a person, we usually do so under more flattering circumstances. People are putting their best foot forward, and trying to make a good impression.
When you think about it, our first interaction with a blog is similar. We see a link from MegaPundit that says, "Great takedown of Marty McBlowhard here." We think, hey, it's about time someone told McBlowhard where to get off and follow the link. We start reading, and think that the writer must be some sort of undiscovered genius for all this time. Of course, this is likely one of this blogger's better pieces, since it was chosen to be linked by MegaPundit, and we followed the link mostly because we agreed with the summary.
So we start visiting the site daily, and eventually the writer will say something we disagee with. That's fine. But then she'll use the same rhetorical tactics against some cause we believe in that she used in her takedown of Marty McBlowhard, and we won't think it's so clever anymore. In the meantime, we'll see a link to a takedown of Wendy Windbag, who we dislike even more than Marty McBlowhard, and read him for a few days.
I think this pattern applies even to our own writing sometimes, which is why some blogs (including this one) flicker out after a while. Sometime we get tired of sound of our own voices, and stop thinking our perspective is all that unique.