Ok this may seem crazy, but check out Google+ again. It is a really nice mix of broadcast and communities (when you can find a good community). It won't replace your FB or your Twitter, but it seems to have a solution to this one niche.

It has the directed-edge-graph of Twitter and also really strong support for communities and pages. I know a lot of the developer communities on there are really strong (I work on Developer Relations at Google so I see it all the time).