Well, if you exclude MonoGame, most of the platform specific code is some window handling (showing messages boxes). The accelerometer, touchpanel, etc... is all handled by MonoGame and even though we contributed to it, it's not technically the core of the flight sim. That's what I counted in the 100% :)

For the UI, it's a custom toolkit we built on our own, so it's 100% similar for both platforms.