Andy Beal has quoted Andy Boyd on Google merging blog search with natural search results. Andy Boyd also has screenshot of a page in which blogs were shown as results after the Top 10. He says that:
I think is new. Tell me if it isn’t. Unfortunately it didn’t seem to work for searches about mortgages, dental plans and mesothelioma.
That's because it's neither new nor is it uniformly followed by Google. The search engine probably has been experimenting with it for quite some time now. Previously even a few blogs were seen in top results but the factors of ranking were unknown. Given that the same algorithm can't work for both websites and blogs, some other criteria as traffic or number of views per post has to be devised.
Given that Yahoo! has integrated Yahoo! Answers with natural search results, it is not question whether but when Google will incorporate blogs into natural search results.