When you count words rather than edits most of the content in Wikipedia does indeed come from contributors outside the core, but Wikipedia does have a lot in common with traditional publishing organizations.
A. Russo, and D. Peacock. Archives & Museum Informatics: Museums and the Web 2009, (2009)Under Creative Commons License: Attribution Non-Commercial No Derivatives.
L. Friedman, and H. Friedman. Working Paper Series, Zicklin School of Business, Baruch College, CUNY; Graduate Center, CUNY CUNY Brooklyn College - Department of Economics, (2008)
F. Fuchs-Kittowski, and A. Kohler. WikiSym '05: Proceedings of the 2005 international symposium on Wikis, page 33--39. New York, NY, USA, ACM Press, (2005)