A good blog post is in essence a question; purposefully opinionated, or better yet, outright wrong. It demands interaction.
The blogger's job is to provide the question, provoke debate, and invite the community at large to pool its immense knowledge and take the conversation further (which characteristic distinguishes the blogger from the journalist). The conversation is the reason why we prefer blogs. If it weren't for the dialog between writer and reader, we may as well just pick up a newspaper or listen to the damn radio.
This is how it was always supposed to be. But typically, either this does conversation not really happen at all, or else it is so slow and disjointed as to suck the life out of the whole process. Blogging platforms and the blogosphere as a whole have failed miserably at enabling effective conversation.