Yes you're right about that Setphen. Definitely Godin is very loved and the bloggers have used their speaking platform to promote themselves. If a person claiming to be a media expert pitched me I think numbers would be important as Mike says. It seems that we don't have enough information for the definitive answer of how to analyze the numbers connected to social media tools yet. Maybe in another 10 years. :)
The Gladwell book, the Outliers, suggests that it takes something like 10,000 hours or 10 years of dedicated work experience before someone should be considered an expert at what they do. So if you agree with that suggestion then that means that in social media there is no such thing as an expert yet. Why? Because the internet itself is just a little past 10 years old. And the technology that allows us to talk like this is still very young. In fact for me, this is the first year where I feel that the tools for blogging have improved so you don't have to be technologically inclined to learn how to use it.
I think that the best we can say right now is that there are some people who have made it their job to understand the social media tools and to develop by trial and error some of the policies that we now acknowledge as best practices. At best a person could be considered an "expert student" of social media as we continue to discover what the tools can do and if the people who are our listeners will indeed listen to us in such a way.
It stands to reason that someone like Godin would have a huge following for his blog and all. He already had a huge following of interested people from his book writing and speaking. I follow Rowse, Brogan, and some other people who I found while browing the subject of social media. I had never heard of them before but their content is what kept me coming back. So it does stand to reason that their following would grow to the present levels. The one thing that social media makes evident is that anyone who has something revelant to say can be heard by the people who want to listen. Before Web 2.0 if a person had a relevant message there was still the issue of getting the publishers/media, etc, to send it out for you.