Don't sites like reddit, stackoverflow and twitter have an equivalent effect? (And I recall Google coming about before blogs. How did Google kill them?)
Google was founded on the answer on how do you deduce the value of a site based on an ecosystem of personal pages around it. (Blogs are simply what replaced personal pages later.)
Have you ever seen any study like that for reddit and twitter? Those have completely different characteristics. (SO looks similar enough, but it's not comprehensive.)
On how did Google kill blogs, looks like you haven't noticed they decided to concentrate their search results on a small number of sites a few years ago.Google just does not lead people to them anymore.
