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Empezado por Casimiro Notevi

Creo que no he entendido: sí, seguramente android está desarrollado en lenguaje C, como cualquier sistema operativo, digamos que es lo normal. Pero se creó para que corriesen programas hechos en java. Lo que no acabo de entender es que (según tu comentario de antes) ocupe más el programa (app) en código nativo (C) que en java, salvo que no se cuente con que necesita un runtime.
Resumiendo, que no me ha quedado muy claro ni me ha parecido muy lógico.

Desde la web original de Android

Android NDK

The NDK is a toolset that allows you to implement parts of your app using native-code languages such as C and C++. For certain types of apps, this can be helpful so you can reuse existing code libraries written in these languages, but most apps do not need the Android NDK.

Before downloading the NDK, you should understand that the NDK will not benefit most apps. As a developer, you need to balance its benefits against its drawbacks. Notably, using native code on Android generally does not result in a noticable performance improvement, but it always increases your app complexity. In general, you should only use the NDK if it is essential to your app—never because you simply prefer to program in C/C++.

Typical good candidates for the NDK are self-contained, CPU-intensive operations that don't allocate much memory, such as signal processing, physics simulation, and so on. When examining whether or not you should develop in native code, think about your requirements and see if the Android framework APIs provide the functionality that you need.

http://developer.android.com/tools/sdk/ndk/index.html