Specifically, these sponsored posts are displayed in a way that causes confusion to the viewing user and, I am confident, this confusion is intentional on Facebook's part. As an apt web user with quite a bit of experience with Facebook and the web in general, I still get confused by these posts. I tend to assume they are posted by the friends that "liked" the brand and only in clearly questionable cases, such as when the post is about a bank, do I look close enough to realise it is sponsored content.
Intentionally causing confusion like this is shady, even if legal, and this "feature" of Facebook warrants as much attention as it is getting.
Ironically, this article is applying the same style of subtle confusion that it attacks (claiming that Facebook impersonates users when the author knows that's not technically accurate). But I must commend this article for providing the information in a simplified, easy-to-comprehend manner that is accessible by the average Facebook user. In fact, I may go share it right now...