It’s effective because in this instance their interests align with their audience’s, which is pretty much an ideal situation in such a capitalist economy. Also, I don’t know how much HN costs, but I cannot believe it is disproportionate in the PR and communication budget of something like YCombinator.
Cult, you mean?
And loving it ;)
Bingo! Being open to access, but heavily moderated, is the perfect spot for them. HN is essentially perfect for it's use case and is unlikely to change soon.