If I ever get over that hump, I certainly wouldn't want to make it harder on myself by hosting my own web server. I would want to write, not manage a server, with whatever complications that brings. That's what makes Medium (and others) attractive.
For the second part, I don't write regularly. I don't look for an audience tuning in every Thursday evening. I write when I feel like I have something to write about; when I learned something new and interesting that I want to share, that more people should (or might want to) know about.
This gives me a URL I can share with friends and/or post on sites, instead of telling friends individually or writing a post on a gated community like Facebook. It gives me some of history on what I've been doing over the years, showing a potential employer I've been doing IT stuff out of school as well (very useful as a young professional). It even serves to remind myself now and then, e.g. my IPv6 post[1] I fairly regularly use to check stuff like "what was the maximum address length again".
In fact, not writing regularly might be more useful to many potential followers. If you only write now and then, they can follow you without fearing their inbox/feed will be flooded, and posts are much more likely to be of quality. When deciding whether to follow back, irregular or semi-regular Twitter users are much more likely to get one from me because they are usually more interesting and not a day to day burden.
If the loss of control is worth the gain in ease, go nuts. Or if you don't really care if what you write stays online or under your control forever. Not everyone does. Twitter, for me: I really wouldn't care a bit if that service turned off entirely and I lost my archive of tweets. They just aren't that important to me. Or my Hacker News comments. They're interesting, but I won't be particularly upset when Hacker News finally dies off and they disappear. But my longer-form writing is important to me.
But I think people shouldn't be under any illusions about what Medium is. They're not a group of altruists trying to archive the world's writings for posterity. They're trying to figure out how to make bank. And if they don't, be aware of what will probably happen...