The article is flawed, but his profile still doesn't seem to play by the rules. When I go to facebook.com/zuck there is no option for me to request adding him as a friend. In normal privacy settings you can specific that either everyone can add you as a friend or only friends of friends. I have two mutual friends with Mark Zuckerberg.

So either his profile has some additional privacy setting (i.e., to only send out, not receive, friend requests) or something else is at play (like he has hit the friend limit -- I'm not sure what that looks like, to be honest).