Chris Randall Interview
A lot of this is quite technical, but there's an interesting discussion on app pricing on the end.
TLDR - basically it's very hard to make money on any platform, and Chris says he only really has a viable business because he can generate plugins for OSX/Windows/IOS. Audio plugins just aren't a big market, even for someone as established as Chris.
Also - while he grumbles about IOS pricing, he states that he makes about the same amount of money on IOS apps due to how big the market is, as he does on the other platforms (despite charging 10x as much). He seemed reasonably okay with IOS as a platform.