I think not enough emphasis is being given to audience management. If I write a blog entry, it's public for all the world to see, and, more importantly, it's public for all the world to comment on. With Google+, I can limit who can see and comment on my posts.
With traditional blogs, you don't get that sort of fine control. Either you have a post visible to everyone, or it's private and only visible to you. Either you have comments open, or comments closed. Yes, you can moderate comments, but that gets to be troublesome for anything more than a trivial number of commentators.
Google+ takes away all those problems. Your posts are visible to only those whom you're addressing in that post. In essence, Google Plus allows you to multiplex a single blog among multiple audiences by making posts only visible to certain circles.
With traditional blogs, you don't get that sort of fine control. Either you have a post visible to everyone, or it's private and only visible to you. Either you have comments open, or comments closed. Yes, you can moderate comments, but that gets to be troublesome for anything more than a trivial number of commentators.
Google+ takes away all those problems. Your posts are visible to only those whom you're addressing in that post. In essence, Google Plus allows you to multiplex a single blog among multiple audiences by making posts only visible to certain circles.