Well, I think of own comment website also as public space... Sure that promotion can help to increase the audience, but I've also seen a lot of interesting blogs that develops their own audience, with a group of people commenting several posts, something that can be very difficult on HN or Reddit (unless you're Paul Graham or similar)
Mmmm, good point, I didn't though on that.
Anyway, if you have 1000 subscribers on your blog, it seems there's already an audience... For some "corporate announcement" it makes sense to have as much exposure as possible, but for a personal blog I'm still not sure is a good strategy...
It doesn't seems like a very good strategy, though. It seems ok to drive visits from the blog to Hacker News, but not really the other way around (which I guess is what people wanted)