Would you downvote a comment with just a link to a paper about the technology being discussed in the article?
Linking a comment, and linking a journal article are two very different actions. I wouldn't downvote someone who linked to a journal article, but that's still kind of a crappy comment. Give a summary of why you're linking to the article, not a chore for us to try and figure out what kind of point the commenter is attempting to make.
The fear is that without moderation, the reddit-ification of the comments will continue its steady march forward. Hence, down voting comments which don't add much
To me, one of the great things about HN is that someone can post a link without comment, and I can click that link without too much fear of being rickrolled, goatse'd, or some other mental equivalent. In this case, if I wasn't interested in looking at a cartoon, I could decide to close the tab in about the time it takes to read the poster's summary.