The so-called logic borders on being bizarre. The reasoning is sophomoric and uninsightful.

But here is the rationalization they use for penalizing Webmasters who buy links. People often have to justify their behavior as being morally superior or for the good of the whole.

But in this case, the logic is almost satirical.

  

http://www.mattcutts.com/blog/selling-links-that-pass-pagerank/
http://googlewebmastercentral.blogspot.com/2007/12/information-about-buying-and-selling.html

I read the article that Matt wrote and I feel the paid links/reviews were basically spam. Matt has a valid argument with the examples he has found. Wasting PageRank on a paid link/review gives the content even better placement in the search engines when it doesn't benefit the user at all.

AdSense too finances quite a few health-related spam blogs, though...