Are we sure Sony can't find a defense for this?
That depends upon how brittle their security framework is. If the keys to the kingdom are really what the security system is all about, then the design is very poor indeed. Any sufficiently mature design, intended to remain operational for at least a decade, would include a protocol for revoking and replacing keys and cryptographic algorithms.
If I remember correctly, the Blu-Ray system is prepared to be upgraded if the keys which enable it to work should be compromised. As the design came out of Sony, just like the PS3, I expect that the PS3 has the same kind of layered security defense.
But that does't have to mean that the design actually has to work. Let's say a key is compromised: how do you safely revoke and replace it? I remember reading about the Blu-Ray security system, and how difficult it would be to revoke a key and replace it. Since not all Blu-Ray devices are connected to the Internet, and some may require manual intervention for updating them, it may not be realistic to revoke and replace the keys without rendering existing discs unplayable. That would be an extremely unpleasant outcome for consumers.
This could get really ugly.