I have been a user of hotmail for a long time now, and have seen this quite a few times. I just ignored it and I am still one of their oldest clients.I think it is just a way to attract more investors to it,or keep the current ones from bailing out on them.They actually do deactivate your account if not used actively anyway.So they might be trying to promote their site because other free e-mail sits are doing better and they are in a tight spot.
regards
v/man