The reason I didn't devote my energy to that project is because I don't want to develop a product that hinges on a billing mechanism that circumvents the app store, because that seems like it could (perhaps rightfully) piss Apple off, since they wouldn't be getting their cut, and my game would be vaporized at Apple's discretion. Not that there's anything wrong with that -- it's their platform, and they can manage it how they like. But the lack of "subscription" billing for apps probably precludes many larger projects.
That said, there's a significant barrier that even a premium 'niche' app must now overcome aside from generating awareness. Couple this with the app likely having very few reviews, not in the Top 50, etc.. then a buyer will become very cautious. (Myself included). In addition, user review system is broken (1-way channel), significantly less than 20% of customers will leave feedback, and upon uninstalling the app rating defaults to 1-star.
I've been struggling with trying to figure out how to best overcome this as a marketer. It's difficult, costly, frustrating, and the .99 trend certainly doesn't help things when 12,000 apps are battling for 50 slots on a poorly weighted popularity curve.
Perhaps the same would be true of AdSense sales.