Very interesting question, Anthere.
Is there even a generally accepted definition of '''free content'''? A search within the website of the Free Software Foundation yields no results. No sources are cited in the article either.
Perhaps it is time for the Wikimedia Foundation (in collaboration with Creative Commons and the FSF?) to create a free content definition, and to make a list of free content licenses. In the meantime, it is hard to see this article as being anything but shaky original research.
Erik