YC companies are
not given preferential treatment, with three exceptions, which are clearly defined in the FAQ (
https://news.ycombinator.com/newsfaq.html): Launch HN posts (
https://news.ycombinator.com/launches), job ads (
https://news.ycombinator.com/jobs), and alumni usernames being displayed in orange to other alumni.
Other than that, YC companies have to compete for attention on HN along with everyone else, and I can tell you that most find it maddeningly difficult.
In some ways we use moderation power to YC startups' disadvantage - we moderate criticisms of YC startups less, not more, than usual (https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...).
For example, the tedious angry-generic-repetitive sort of subthread that tends to get upvoted on most common topics is exactly the kind of thing we downweight as part of standard moderation, but we do that less when a YC startup is the topic. That's not because such discussion is any higher-quality in those cases (it isn't), but rather because people are quick to jump to the conclusion that we're doing nefarious things and we need to be able to answer those concerns in good conscience.
The fact that there's all this drama about one such subthread having gotten downweighted is actually an indication of how we don't do that. It happened, but only by mistake.