Anyone can sacrifice margin for market share. That's easy. The point is to maximize profits and that's what Apple does, hence why Apple rakes in 70% of the profits in the entire mobile phone industry.
Market share matters only up to a point and that point depends on your business model. Apple is a hardware vendor - that's how it makes its money. For Google the thing that matters is market share because they need eyes on ads and to be able to get their hands on data. Those are both perfectly legitimate business strategies, of course.
Now, I know what people will say - if Apple fails to hold onto the largest market share the platform will lose dev support. Well, in reply to that I say: WWDC sold out in 90 seconds. Clearly the slide in market share isn't putting off the developers who still make far more money from iOS than Android.
Plus, iOS is bigger than iPhone. If you combine iPhone, iPad and iPod Touch sales you've got hundreds of millions of customers per year and these customers buy apps and surf the web, unlike Android owners who appear to do sod all with their tablets.
1) Quoted as people should really read this and understand it
2) Motorola went down the marketshare path. If that doesn't give you pause, I'm not sure what will. Heck, Motorola isn't even on the list now, they're clumped into "other."