What's in a comment?

I've been looking at a lot of blogs lately and I can't figure this out.

What makes people "post a comment" for some entries and not for others? There are some blogs that have amazing information and no one comments while others will write a seemingly basic entry and all kinds of comments show up. I haven't found the relationship between the two yet and it's not important to my personal blog.But, I would like to know since I have started a wiki and will be starting a blog at work for some of the information our department.

Perhaps I'll make a little study to see if it has to do with the person who wrote it, how personal the entry is, how interesting the topic appears or if it just has to do with the moods of people reading the entries.

Any thoughts? (Ha, maybe this the key - asking for something in the last line)