People get immediate value out of Angie's List: Vetted services. Angie's List has an actual story--everybody's had a terrible experience with a plumber, electrician, or other service. Not everybody has had a terrible experience getting data out of Twitter. Most people really don't care about that.
I think there's a vast, vast difference between the two.
If the early members of App.net built a great community and become a good resource, regular people would pay for it.