I've read a couple of interesting blog posts this morning [Talei Loto, Jody Hedlund] about why a blog reader takes the time to post a comment rather than just read and move on. I'm definitely guilty of skimming blog posts and not stopping to comment until one really strikes a chord. I probably do read your blog. If I haven't commented, it's might be because:
1) It has a lot to do with my introverted personality. In face-to-face conversations, I usually tend to be more of a listener than a talker, unless I'm really passionate about a subject. The only problem is, when you're online a blogger doesn't necessarily know you are reading/listening (or even who you are) unless you post some kind of written acknowledgement.
2) Sometimes, I can't think of anything clever thought-provoking to say, and since another commenter has already taken my standard "Great post!", it seems redundant to repeat it.
3) There's a time factor. I read a lot of blogs and it takes time to post. Some blogs still have those verification boxes where you need to type in a nonsense word and may not seem worth the effort when all I'm going to say is "Great post!"
4) I do comment when a post sparks an idea. Perhaps, as I read more blogs, I'm becoming choosier (or lazier). If I don't come across a new way of talking or thinking about something, I don't always leave a comment. This reminds me of how an agent or editor has all those submissions to read, but doesn't respond unless one really catches their eye. It just shows that, like writing a novel or a query, showing some blog personality or originality is important if you want to get more attention.
EXCEPT, when I think about how much I appreciate the comments I get on my own blog, especially for posts where I've taken time to compile a lot of links or spent a long time working on what I want to say, I can see how, in a way, I'm letting my fellow bloggers down when I don't take the time to comment.
As a writer, I often don't know how others react to what I've written. But when I do, wow! It can just make my day. In a way, a comment, no matter how short or simple, is really saying, I appreciate the time you've taken to write this. I'm reading your words.