The line I think between blog and many other media sites has blurred, but to this excellent list I'll add a few FWIW:

-It both educates and entertains. We can go anywhere for facts, perspective so that's what I read (and try to write). 
-The community is strong. Both the blog host and the others in the discussion are there for me than "good post" and 'here's what I wrote link bait' - they aren't just doing social, they are social.
-It's real, practical, approachable. I read so much that's just 'content' and wonder how did that run on LI or HBR or one of the bigger SM sites? You and I've written better. Too many blogs are either too light, barely touch the surface; too much choir preaching to the kool-aid drinkers (seen it on a few of the few corporate blogs/social profiles I follow); just not enough 'there' there.