They aren't paying YC for most of it. I expect those types of pieces rise due to excitement about the process or the particular technologies used

For example, some posts talk about Puppet or Chef in the title. I didn't recognize those the first time so I look. Having learned something, even though others may know all of the embedded content, I up vote. The next time I may skip over it, having already went through the discovery process, but other people come across it and derive value. Hence the cycle continues.

I doubt they're actually paid, but it's wise to remember that Hacker News is intimately connected with Y Combinator. It's partly a vehicle for the companies to get feedback/criticism, and thus to some extent, promote their products. YC companies are allowed to post job listings which aren't able to be flagged or commented on. It's just a part of the culture here. Whether it adds value is a personal matter. For me, it generally doesn't, but the overall discussion is of high enough quality that the small amount of noise those generate is worth it.