If you're making a great product and you choose to make sure you don't get traction by taking this route (assuming you're not in one of the few niches where it might be somewhat viable), you're just making sure you don't succeed and that worse products with better advertising are relatively more successful.
Hacker News does not advertise because it is a gigantic advertisement for YCombinator. This is not some sort of scurrilous accusation, they may not be constantly banging the table about it but it's not a secret.
Hacker News does not depend on me buying products from it for it's survival. If you can't see the difference in why a company cannot depend on word of mouth, then you're just really not trying to have an honest conversation.
Hacker News depends on a constant stream of new users to keep the site alive, just like any other discussion forum. But you're right that unlike the average company this site seems to be OK with a stable but small user base and isn't aiming for unbounded exponential growth.
It's the way it used to be done with paper catalogues. If you're looking for a snowmobile then you go get a snowmobile catalog from a dealer who you looked up in a phonebook. But advertisers don't want to wait for somebody to decide they want a thing, they want to brainwash otherwise content people into wanting something they didn't previously want.