You're leaving out the "official" counterpart- Direct3D drivers. Microsoft and hardware vendors both have an active interest in adding support for new versions there.
Microsoft has interest for pushing new versions only in new OS releases and uses that to push these new OS releases - see DirectX since 10.
GPU vendors do not care, they will give you API to their hardware for any OS version that moves their wares. That's why I would trust more GPU vendors than OS vendor.
GPU vendors do not care, they will give you API to their hardware for any OS version that moves their wares. That's why I would trust more GPU vendors than OS vendor.