My understanding is that high-karma accounts can downvote comments/posts. HN is still primarily a community where supporting & encouraging those building things is the norm. Criticism of makers isn't rare, but my hunch is that it's less accepted. So this could explain the downvotes. Also keep in mind that HN is still a work in progress—to this day. Dang works hard to keep a civil, supportive community, and how upvotes/downvotes get weighted could be at play too.