Bradley Horowitz, an old friend from my AltaVista days, and one of the smartest guys I know uses this simple illustration to convey the idea.
I have seen this natural hierarchy many times. My experience with SiliconInvestor, one of the first investment discussion boards on the web, matches these findings. The contributor to commenter to reader ratios were about the same. Later at Napster I saw a similar pattern. Very few people shared their music collections while millions downloaded.
Web 2.0 social network sites are finding the same thing. It takes a relatively small group of contributors to create the content. These contributors attract the commenters or editors, which in turn attracts the huge audience.
At Wikipedia about 50% of all article edits are done by 0.7% of users, and more than 70% of all articles have been written by just 1.8% of all users, according to the Church of the Customer blog (http://customerevangelists.typepad.com/blog/).
Fred Wilson says his vision for social media is; "every single human being posting their thoughts and experiences in any number of ways to the Internet." TechMeme has picked up Fred's post, contributors are sure to follow, and thousands of readers will enjoy the benefits.