The Mashup Business

How does one make money by producing a useful mashup? Right now the answers seem to be limited. Other than being paid through advertising, lead generation/affiliate programs, or a transactional based model. There arent many currently in use. Those that are in use have 1 thing in common. They rely on the some outside party to pay in. And when they dont, they result in lawsuits and/or cease and desist letters. Is this property inherent in a mashup? Or are there other ways to mashup mashups and business.