In reply to The Sorry State of Native App Typography Licensing:
A book is a static text, and the font is not being 'used' by the reader of the book. A font embedded in an app is, typically, being used by the app or by the end user in a variety of ways, e.g. displaying dynamic text or actually creating text. This is pretty straight-forward code licensing from the perspective of an app developer, like licensing an API or DLL. There's a pretty basic cost/benefit analysis to be made that is the same for fonts as for other embedded code: roll your own, license from someone, or find an open source or free option.