This is awful advice. Our blog has, on some days, received more traffic than our actual site. In addition to generating sales, it has also helped us substantially with SEO and connecting with our users.
This is quite possibly the worst advice I've ever seen on HN in recent memory. Just because you can use facebook/twitter et al doesn't mean you can't have a blog. They aren't mutually exclusive. One word of caution, if you're spending tons of time on your blog with very little to show for it, maybe consider getting rid of it or cut down your post frequency.