I'm not quite sure I understand what CNET's rating has to with the "optional update". Were you looking to understand why update KB972696 was recently classified as "optional"? If so, I suggest you read the various explanations given by the Security Essentials Forum Moderator (Stephen Boots), within this thread. Hopefully, it will help.
If the above is NOT the case, please post back with a few more details. It will help us, help you. Thanks!
If CNET rate MSE in top 5, why does Microsoft class updates as optional?