Maybe this is all part of the soft marketing for YCombinator backed companies so they get technology "mind-share".
The 42Floors blogposts are generally good quality too, so nobody has any reason to flag them, and they're generally on topic and somewhat interesting, like this one.
What next? Send out internal emails saying "Hey, the company has just posted a new blog, but you don't need the actual link, instead just use the HackerNews one, or maybe this Reddit one..."
I'm pretty sure any company featured on HN (eg RethinkDB or any other) would send a link to the comments on HN if their product was being discussed here, and most employees would then upvote it.
It is a voting ring, but it's probably not done maliciously and it's just how HN works, I guess.
I suspect the "friendly upvote effect" has a lot to do with getting to the front page (which admittedly is important), but that doesn't make up for low quality content.