CNAME support kind of conflicts with "Not hosted by us, so when we go down...": When your DNS goes down (e.g. you are using your blog to inform your users about transferring webhosting from one provider to the other) your blog will also not be reachable.
For this it could be wise to have company-blog.com besides company.com.
For this it could be wise to have company-blog.com besides company.com.