Blogs have no special powers of high rankings. What they do have (if done correctly) is fresh, unique content. Search engines do tend to like that, regardless of the format. If they know any given site is adding new articles on a frequent basis, they will come around often to index it. Blogs are certainly one way of easily adding new information to your site. Newsletters archived on your site can provide a similar benefit, as can archived press releases, or a popular forum.
The "pinging" done by most blog software these days also seems to help get blog posts spidered and indexed very quickly, which is a plus. In addition, blog posts will also show up in blog searches such as Google's Blog search, and Technorati Blog searches.