I'm a moderator of a fairly large (600K) subreddit, and it's relentless. We have to keep upping the minimum karma req's to post but bots just start acquiring more and more. It's a never ending battle.
I wouldn't be surprised if the HN team is already doing a lot of work already. Another factor that may have spared the HN community is that there are lower hanging fruit to pick first, reddit being the prime example.