As Kwpolska pointed out, Launch HNs are a different category of post—they get a guaranteed initial placement on HN's front page, though after that they rise or fall with upvotes. They never get placed at the top, though.

Launch HNs are one of the things that HN gives back to YC in exchange for funding it. The other big one is job ads for YC companies. This is in the FAQ: https://news.ycombinator.com/newsfaq.html.

I believe “getting on top of HN” is a given for those Launch HN posts.