I think you're underestimating the amount of platform-independent code in a typical app.
Looking though a random sample of non-game apps on my iPad, I'd guess that about half would have a significant chunk of code which is not OS-specific, including: Gmail, Spotify, Anki, Google Maps, Facebook, Twitter, Penultimate.
I also don't think that the choice between C and Java as the common language is so clear cut. C would get you some speed benefit but Java has GWT for porting Java to Javascript, and and a huge range of other tools and libraries. In the end I think it would come down to how comfortable your development team was in each language.
Looking though a random sample of non-game apps on my iPad, I'd guess that about half would have a significant chunk of code which is not OS-specific, including: Gmail, Spotify, Anki, Google Maps, Facebook, Twitter, Penultimate.
I also don't think that the choice between C and Java as the common language is so clear cut. C would get you some speed benefit but Java has GWT for porting Java to Javascript, and and a huge range of other tools and libraries. In the end I think it would come down to how comfortable your development team was in each language.
(Disclaimer: I'm a Java developer)