Why doens't ATI post new drivers to Windows Update/ Update Catalog

When you use Device Manager to check for a new ATI driver, in this
case for an x1600 Pro, Windows Update reports the latest version is
installed version 8.391.0.0 dated 6/26/2007.

But according to ATI's Web site, the latest version is 8.9.

Why doesn't ATI push the latest driver to Windows Update -- so it
would be easy for everyone to make sure they have the latest driver --
and to easily install it?