Why do we need science blogs?

…when we have official web site?

…was the question of my supervisor after I finished this , which made long discussion with other IT professionals who tried to understand what I was talking about. Really: why do big organizations, intitutions, universities, D-libraries, E-consortia, need their blogs if they have official web-site with all information presented? I know the answer on this question, but I would like to hear/read from you, IT people, why do we need science or edu.blogs so that we have not only second, but third, fourth..etc. opinion.