You seem to keep using examples with friends or buddies, and no one is gonna fault you for sharing a link to your buddies site from your site, especially if you say "Here's my buddies/friends site...you should check them out"..thats genuine

the problem here is they are/were promoting a campaign in which they were asking you to specifically place "beiber" links on your blog, so that they get better page ranks in google.

you and you're buddy (or even a celebrity helping out their friend for free) are trying to share a particular link with your blogs viewers, and that single instance will probably not have a crazy effect on google page rank

RG is trying to game the system by getting bieber backlinks on a bunch of blogs in trade for a tweet...thats against googles rules