I make the links inactive to ensure spammers get no traffic, and thus give up spamming us. HN gets so much traffic that otherwise they might get a significant amount just from people clicking on the dead link. Anyone who wants to see the url of a story can see it on the edit page, e.g. https://news.ycombinator.com/edit?id=3146776

As for your specific examples, the first was killed because that user is banned from submitting, and the second I killed myself because when I tried the link it was broken; it's since been fixed so I unkilled it.