Writing HN comments is much easier than writing blog posts because the inspiration is the story that's been linked to; for a blog post you don't have that starting point, you just have a blank page. That's a heck of a barrier for most people when they're starting out.
 I know. I did it on purpose.
It's incredibly hard to search HN comments via search engines too, but I've definitely come across comments that just made me stop and think.