Some people link to archive.org to future-proof against dead urls.
In this case the archive.org link is a 403 for me while the original works.
When you make a posting on HN or anywhere else and cite a URL, that URL could go down years later. Your historic posting then has a dangling URL. You can't go back and edit old postings to fix it.
Also, some content changes. The URL is valid, but the cited material is not there. With the archive, you can point to a specific date when that was retrieved.