I copied that from Wikipedia (back in 2007 obviously) public domain release statement, which is written by a lawyer so I've no reason to believe it's not watertight, at least in the US. The intent is to make it public domain, but unfortunately you can't "place something in the public domain" in most jurisdictions, contrary to popular belief. Therefore you have to provide the back-up extremely liberal license. Nowadays as others have said you'd be better off using CC0.