Announcements will be used for those small updates that aren't really large enough for a news post. Although if you've read these lately. You'll notice just how often I post about small things like this. I digress.
You will notice in the future that these announcements may link to news posts related to the announcement itself. All-in-all, it's just about making sure the super important statements are seen by nearly everyone and not just the news-savy few.