And like I mentioned, we don't have the possibility of raising the PR of the subdomain by linking to it from the root domain, because we don't have much room on the root domain for editorial content where we could link to the blog.
Regardless of where you host it, if the blog is important to your business why wouldn't you make space for a simple link to your blog? How much space does a text link saying "companyname blog" really take up? Do you have a footer section on your site?
[edited by: MadeWillis at 4:10 pm (utc) on June 10, 2009]