Maybe pg considers HN essential. You don't outsource your main business.
Maybe developing and mantaining HN is one of pg's few connections to his developer side.
Then where would he go to do his share of procrastination for the day?
I tend to think that PG considers maintaining HN as his hobby, he enjoys keeping this knowledgable piece of work for himself.
What revenue stream would he pay this person from?
Now, I can't profess to know pg's reasons for not doing that, but he definitely shouldn't! Why? This would start him on that long, slippery slope of becoming a manager, i.e. the sad metamorphosis from a hand-on, still living technology throughly person, to one who interacts it secondhand, through ideas only.
Look around in any large company, you will see these guys who were once brilliant engineers but now just don't have the time to code.
Unfortunately, with YC getting bigger and more prominent by the day, I think this may be inevitable.