It's certainly there to promote Scribd. I don't believe that HN has ever claimed to be an independent, impartial site. It's on a subdomain of ycombinator.com, it is heavily frequented by people who are either involved in YC, or people who want to be. Any story that is linked to a YC company is going to get a disproportionate amount of attention here, and I doubt that YC will hesitate to integrate links/widgets from YC companies as they've done with Scribd, CO2stats, and others.
I'm pretty sure that one of the purposes of the site is to attract people to YC. If you want to know why people like myself (who are just here for the hacker news/discussion) stick around, it's because it has some of the most interesting and civil discussion of any online community, and if you know about the YC bias then it's not a big deal to filter it out in your mind when browsing/reading the site.
Maybe "unethical" is inaccurate, but I did mean to make a strong point. How about "annoying and unnecessary"? One reason why I enjoy HN is because, as you said, the intelligent and civil discussion. Despite it being sponsored by YC, I really appreciate the distinct lack of advertisements or blatant links to YC funded apps. It truly feels like an inclusive environment for all hackers, not just YC affiliated ones. Your comments are judged by their content, not (usually) by whether the author is part of the YC clique. Yes, I understand YC doesn't owe anyone anything, and if they wanted to, they have the right to turn HN into a billboard for YC companies. But that's not why I come here. That's why I think HN should nip these trends in the bud, so it stays as inclusive and impartial as possible.
I'm pretty sure that one of the purposes of the site is to attract people to YC. If you want to know why people like myself (who are just here for the hacker news/discussion) stick around, it's because it has some of the most interesting and civil discussion of any online community, and if you know about the YC bias then it's not a big deal to filter it out in your mind when browsing/reading the site.