Cable TV has a much better value proposition than a Twitter alternative. There's no free alternative to cable TV with a comparable feature set.

I do think it's an exaggeration to say that app.net caters to the rich, but I can guarantee you that the demographics skew much more upper class, between being an app that is charged for and a service that mostly has interested hackers (who, nowadays, tend to be an affluent bunch, for better or worse).