You have to look at a number of factors. First, some sites are using blog platforms at a content management system and aren't really blogs. So when you get that out of the way you can look at why Google likes the blogs: real time search and social media web 2.0.
Real Time Search and the recent updates to it in December is one factor. But more important is that Google loves the Web 2.0. It's also easier to build links with a blog; because, the webmaster has the "blogosphere" to work with and many tools such as blog rolls, trackback, rss feeds, etc