"Wikipedia does not publish original thought: all material in Wikipedia must be attributable to a reliable, published source." (I read that at Wikipedia.)
"Wikipedia's standards of inclusion--what's in and what's not--affect the work of journalists, who routinely read Wikipedia articles and then repeat the wikiclaims as 'background'..." I just read this here at Technology Review by Simson L. Garfinkel.
When the published source relies on Wikipedia content, the paradox arises.
If journalists continue to cite Wikipedia as a source, and Wikipedia links to those articles for reliability, then Wikipedia ultimately will use itself as a source, something its rules forbid: Catch-22.
How this hasn't happened yet, I don't know, but it should happen soon. But I do know that when it does, Wikipedia will vanish in a puff of logic.1
Eventually Wikipedia "verifiability" will be supported entirely by sources citing Wikipedia in one form or another, essentially citing itself as expert.
We can only hope that the resulting anti-net ("anti-Internet," think antimatter) black hole won't suck us all in. (But I guess if it's a black hole, it will.)
1 What happens to God in The Hitchhiker's Guide to the Galaxy.