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.
It's a lot easier to find other people on Google+ based on interest. When I started using it, very few of the people I knew already were on there. I was able to search for other people interested in videogames, anime, programming, etc, and rather quickly I was part of a fairly large group of people reading and commenting on each others posts.
Discovery in Facebook is centered around groups and pages, which have a higher UX cost compared with posting a status update. On Google+, you can be found by anyone right away. And people use the sites differently because of this.
People make public posts on the assumption that what they write will be found by people they don't know yet who are interested in what they write. Facebook status updates on the other hand are usually always intended for people that the poster already knows, whether posted publicly or privately.
In the time I've been using Facebook, I can't recall once being friended (or now subscribed to) based on interests (as opposed to some existing connection). On Google+ however, I receive a new asymmetrical follow almost daily - and I'm someone with a rather low posting frequency.
This is what makes Facebook and G+ different.
Thankfully my friends and I share many common interests, but that's a very limited audience. So I run my own blog where I post things that my friends might not be interested in, but someone will hopefully be interested in.
Then, I realised that Google runs Youtube, remembered all the recent changes in particular, my face turned green and I puked up a little inside...
If they can mess up such good service when it was handed to them on a plate, I have zero confidence in them in any new endeavours online, especially when the cost is my privacy for perpetuity.
So, thanks but I'll continue to stay well away from social networking sites.