As I hinted at in my brief post yesterday, I haven't seen any actual data that would support the model being feasible outside of games in the App Store. I love seeing innovation like Paper but it's not clear to me if their business is about Paper or being a creative agency.
If you go look at the top grossing in categories such as Productivity, Finance, and Navigation...most of the highest grossing apps are paid. And those that are free, are produced by big brands or startups that have the ability to promote like crazy and upsell both in and outside of the App Store. The app is an extension of their brand or service...not the product itself.
Jeremy Olson