Jack, Jack, Jack. I think you've missed the point. That is, if you are looking for wisdom and knowledge. If, on the other hand, you are simply looking for an argument, then I believe I'm supposed to start out by saying something that LZ would delete when someone pointed it out to him.
Um, intentions, reality, and perceptions are very often three different things. And, if there is more than one person involved, you can even add additional perceptions to the mess. I have no idea what LZ had originally intended for the blogs and the forums. It's quite possible that he never had any intended use; he simply set them up because the people who came to his website asked for them.
In my experience -which I recognize may be different from yours- the _blogs_ tend to be bombastic wastes of space, mostly "Hey, everyone, look! I posted another chapter." And, as a matter of results, the blog entry announcing chapter 12 shows up on the home-page stream AFTER the actual chapter 12 entry shows up, making it of absolutely no value to anyone. Of course, as you pointed out many of the blog entries do say something useful.
On the other hand, what I've seen of the forums is more of a question and answer session. There are a lot of rants, but mostly it's been people asking questions. And people giving answers. Not always even on the same subject much less actually helpful, mind you, but answers.
With that in mind, I'd suggest that you have it exactly backwards: The forums are for the thoughtful while the blogs are more for those who just want to talk and they have no interest in any answers.
The truth (as I see it) turns out to be orthogonal to intention. It has been my experience that my blogs are generally answered by readers with a few writers tossed in, while my forum comments are generally answered by other authors, with an occasional reader who got lost. So, these days I use the blog to talk to my readers while I use the forums to ask questions of the other authors. Read whatever you want into the sorts of answers I get.
-ZM