Why is it in Apple's best interests for your app to run on iPhone? What competitive advantage do they lose if your app--which doesn't depend on anything special

Why is it in Apple's best interests for your app to run on iPhone? What competitive advantage do they lose if your app--which doesn't depend on anything special--runs on android, palm, and blackberry but not on iphone? Er, because then there wouldn't be much left? The large majority of iPhone apps don't depend on anything "special"; just touch events, basic widgets, and sometimes accelerometer support and 3d graphics.