Windows security advisories are surely important to quite a few people, and probably to more readers of -devel-announce than Ubuntu stuff. Are you saying that it would be okay to post these? If not, then you need to rethink your reasoning here. Personally, I don't think "important to the subscribers" is the correct measure.
But Windows security advisories don't contain debian packages. Ubuntu does contain close to all debian packages, and (I hope) most DDs have an interest to include improvements of other distributions in their packages (at least I do).
Willi