PR can be the same as in Blogger or professional domain .com. It ranks only in case you have built a good backlinks to them that's why it rank.
I think you're asking for blogspot blog ranking factors Read these tips http://www.google-success.com/seo-tips-for-blogger-blogs.htm
PR is ranked by page and not by domain or sub domain. So it doesn't matter whether its from a Blogger or Wordpress or other domains.