Available to everybody by clicking on the link labeled “past” at the top. I don’t know why you chose to highlight those specific four submissions – only one of those received any comments, and that one got a total of three comments.
What's happening is it's getting a lot cheaper to buy votes on Hacker News. People have offered to do it for me to get the O(n) search papers I resubmit every quarter to the front page. Folks assure me "it's way cheaper than it used to be!"