People are confusing this master key that breaks HDCP, saying it can help decrypt Blu-Ray discs. That's not the case: Blu-Ray is encrypted with AACS, which has a similar concept of device keys derived by a master key. AACS has a mechanism of revoking compromised device keys. Getting the AACS master key would bypass that mechanism, and would be great news.
This key isn't the AACS master key This is an HDCP key, which would allow one to create a "unauthorized" device that can connect to HDCP-encrypted HDMI and succesfully decrypt the HD stream.
HDCP has been known to be nearly broken since 2001, in that obtaining the device keys of 40-50 devices is enough to calculate the master key.