The goal of a prototype is to prove in the real-world some of the key concepts upon which the BusinessModel will be built.
But the goal is also to gain more concrete knowledge to feed the construction of the BusinessModel. So it makes perfect sense to build a small-scale prototype even before the BusinessModel is refined. Some even say that if you build a prototype that can fly, then you can build a business model later. Let's just say that it can not be bad to have a certain feeling for the most promising runways.
A BarCampBank Workgroup