Copyright is owned by the writers; HN has implied license to display. (This has come up before; fairly sure I am quoting a lawyer.)
[Edit to add: https://news.ycombinator.com/item?id=3641312 <-- Grellas is, indeed, a lawyer.)
[Edit to add: https://news.ycombinator.com/item?id=3641312 <-- Grellas is, indeed, a lawyer.)