This is because $#@!!!! spammers can screw up anything. I have to disallow anonymous comments, or I get a bazillion blog spam comments, I check comments a week later, and there's 200 of these that I can only delete 10-20 at a time. Annoying to say the least.
How you can comment is to register a user for our blogs. You don't have to have a blog here to be a user. I know it is annoying to have yet another user-password pair to remember, but this is the best I can do.
The second thing you can do is send me e-mail. I try to respond quickly to e-mail posted via the blog, and if you want it added to the comments, just ask. Sometimes when people ask really good questions, it turns into a whole post, which is good for everyone (actually, this is an example).