Ask HN: Economies of Scale in Multi-Platorm Mobile Apps?

I'm interested to know if there are any economies of scale possible in mobile app development. I want an app developed for iPhone, Android and Symbian (or whatever that is morphing into), but should I expect that each will begin with a clean slate and be billed accordingly? Or are the lessons learned in a first iteration, of ie. an iPhone app going to save a developer time on subsequent platforms?