This reply covers it a bit and links to the law enforcement document Apple referred to: http://empegbbs.com/ubbthreads.php/posts/366035

Apple is defining unlock in that question as "Has Apple broken encryption or brute forced a PIN for law enforcement in the past?". Apple is stating that no they never have.

Apple with every iOS and iPhone release has continued to protect data on the device to prevent extraction (of already decrypted data) via methods both they, and 3rd parties were employing.