Yeah, because we should never, ever be subjected to the same content twice. After all, this is Hacker News, not Hacker Olds, amirite?
(Sorry for the snark. I have been reading Hacker News for several years, and I don't recollect having read this article before. I enjoyed it, I upvoted it, and I'm glad it was reposted.)
In any event, there's no way to block resubmissions programatically: the site owner could just change the name of the file.
No need to change anything on the webpage.
page content hash
What if you resubmit a blog post that's picked up 150 more comments since it was last posted? How would HN tell the comments apart from the article text?
What if someone submits a blog post that heavily quotes another article that's been submitted, in the process of rebutting it, and ends up being a 80% match?
Most resubmissions are submitted by people other than their authors, who are typically not in a position to change any bytes of the content.
In the present case, speaking as the last person to submit this one (more than two years ago), I don't see that there's any harm in it at all. If this is still interesting two years since it was last discussed on HN -- which clearly it is -- then good for the submitter, who has provided the HN audience with something interesting to read.