GFDL 1.3: Wikipedia's exit permit

GFDL 1.3: Wikipedia's exit permit

That's a good example, but it's also crucial to know whether someone actually did copy Spiegel's slight extensions into Wikipedia; if not, the GFDL didn't help Wikipedia at all; it just allowed Wikipedia to be a dog in a manger.

Assuming someone did, then it's still just an example of Wikipedia made better by copyleft (as opposed to public domain), and still leaves me very skeptical that Wikipedia is made possible by copyleft. To believe that Wikipedia wouldn't exist, or would have substantially different character, if copyleft licensing didn't exist (which seems to be Lessig's claim), I'd have to believe that huge numbers of people who today contribute to Wikipedia would in the public domain case write for the likes of Spiegel instead. I can see that Spiegel could pay more if it had exclusive use of the work, but I don't see it being enough to have a noticeable effect.