If you follow his blog (which you absolutely should, stick in in your RSS feed reader, it's also one of the dwindlingly few places where the "never read the comments" advice is wrong) he's been struggling with eyesight problems and cataract surgery coinciding with book deadlines. Not at all surprising he isn't devoting any of his usable screen reading capability right now to HN.

Ouch, that sucks. Thanks for pointing it out (and I just realised he mentioned it in the first comment on his post as well...)