Why is Netbot free?
1. Gets more people on ADN (seems to be working http://appnetizens.com/nupd).
2. Developer Incentive Program revenue has been ≫ sale revenue and we hope that as more users come in that amount grows for everyone (and obviously us).
Fascinating that App.nets Developer Incentive Program brings in more revenue than the direct sales of the apps for Tapbots.
This bodes well for the platform as a whole because it means popular apps run as side projects could flourish in the app.net ecosystem as this would cover the costs nicely and bring in a small to decent income as well. And with some scale it might even work for more than just side projects.
(Keep in mind that the incentive program does more implicitly for the promise of the platform to developers than it does directly via payments.)
Even if you are only slightly interested in the economics of platforms you should watch closely how app.net is evolving.