Come on. HN gives YCombinator some measure of "street cred" in the tech community, it gives visibility to startups (especially YC's.) It's the water cooler where people gather trying to appear innovative and thought-leaderish just in case sama or pg wander by.
Obviously it's a moneymaker. The goodwill and the brand make money. The low-tech anti-modern anti-business aesthetic makes money. There's a reason this forum is a subdomain of a venture capital firm. I agree that they shouldn't (and probably won't) change in Reddit's direction but only because they don't need to. Why bother with ads when your entire culture is in essence an ad funnel?