The private key was derived mathematically from the public key material because Sony generated its keys wrong. Copyright has nothing to do with it.

There's a good explanation on YouTube (until they're taken down by the gestapo) which is the Fail0verflow team describing their research. They have a section at the beginning describing the history of console hacking and game piracy, or at least their perspective on it. They take pains to point out that most of their research is not even particularly necessary to pirate games but instead to run user-supplied software on the PS3. http://www.youtube.com/watch?v=HEFMAP0mTvY

Incidentally, Sony had previously been sued by Certicom for allegedly infringing on patents related to its use of elliptic-curve cryptography.