Nothing fundamentally has changed about HN as Y Combinator has become more successful over time. Your premise pretends that both HN's long-term and initial success rests on the present riches of Y Combinator - that's false.

HN runs on one server and is moderated by just a couple of people typically. It is in fact the definition of a mom & pop operation. It does not have a zillion dollar budget, either for operations or promoting itself. It doesn't need it, the value proposition is the content, community and standards.

I can semi-trivially set up an HN clone for any given industry or concept. It'll be up to me to promote it and garner attention to it, however the point is that it's extremely inexpensive and easy (few regulations, hurdles, compliance issues, etc) to open up that type of expression platform. That's what the parent is referring to.