I wanted to use this to go off on a slight tangent about an APPs usefulness to the network. There may be many APPs that don’t require PUTs. It’s not that the APP won’t be valuable…it’s just that it won’t be valuable to the direct economic advancement of the network.
The network gets paid every PUT. Therefore any APP that gives that value to the network should be rewarded. This is similar to a comission-based system as @Traktion pointed out.
In that case it can certainly persue another business model - hell, even if it is getting rewarded by the network you can still pursue another business model.