You don't need to use MS's site to post to their Usenet groups
I have never once even signed up for MS's discussion forums, but I post to them on a daily basis. You don't have to use MS's news server -- most news servers carry the MS groups (including older ones that MS has discontinued on its own server). After MS shuts down its own NNTP server, those microsoft.public newsgroups will continue to exist on other news servers and will likely get plenty of activity.