Making end users pay is a huge barrier to entry for startups. Not all can afford it. And App.net is there to play zookeeper, and could shut them down if they do anything out of bounds. For users this is great but for startups it's hugely dangerous. So app.net has a marketplace problem : to overcome this they need to be huge (think Apple App Store huge) and to be App Store huge they need the startups and users.

Disclaimer : We build hull.io. we think that developers need stay in control of the data and responsible for themselves for this to work.