Many people here talking about windows updating the microcode are forgetting that the part of the cpu that stores the microcode is volatile. This means that windows would have to update the microcode on each startup, making this microcode change not permanent.
I don't see this happening at all as the microcode update via windows update has never happend before. There were many times where this could have been done (eg. AMD's TLB bug)
that makes nice reading!
Cheers