It seems that every blog I go to, they can easily be PR 4, 5, or 6. Is it just due to the amount of pages and information that gets built up?
Many factors do play a roll, blog directory links, blogroll links from other blogs, being listed in bookmarking sites, in signature links, in the latest blog feature on this and other forums.
Google does not give a preference to blogs as far as i know. PR is still based on the quality of inbound links.
page rank is not related types of your site . there is no difference between a directory or a blog. pr is calculated with your backlink counts . not types of your site
No, blogs are given no preference solely on the basis of being blogs. However, a blog's very nature ensures that it meets two of Google's most critical requirements: 1. Constantly updated, unique content 2. Backlinks from other sites (usually blogrolls, as was already stated)