Perhaps it's some sort of honeypot by pg to try and increase the signal to noise ratio, ie. everyone who voted that comment up gets blacklisted from HN.
This is the most machiavellian idea I have ever heard around internet community management. You can mercilessly enforce policies while appearing to do nothing at all. Except you dont blacklist them, you just reduce the influence of their votes in the ranking algorithm.
That's what I'd do if I were king :)