When I submitted http://www.facebook.com , it redirected me back to the previous outage link because the URL is the same: https://news.ycombinator.com/item?id=7914905 I added a random URL string to have HN recognize this as a new entry. Perhaps it's a good idea to allow re-posting the same link for certain URLs so that "XYZ is down/having issues" type posts aren't deemed as duplicates?
How necessary are those posts though? A link to a site that is down is practically useless. A link to a blog post about the current status or a post mortem is very useful.