That's because Apple keeps it simple and has 1 iPhone each year unlike the dozens or hundreds (?) of Android phones over the past few years.
If you look at marketshare of android vs iOS its a different story.
Market share isn't the point. Apple is selling more iPhones every year. They are growing. Growing and growing. There is no way that they could maintain the same market share measured in units sold as an operating system which is sitting on handsets they're giving out on a buy one get one free basis.
Based on that argument BMW is making all the wrong choices and Cartier may as well shut up shop and go home. Apple are competing at the high to mid-high end of the market and they are kicking all kinds of ass. Hence their profits make up more than half of all profits from mobile phones. Hence their penetration among high end users who spend more time online (look at mobile browser numbers) and buy more apps (ask Android devs how much money they're making form the Android Market).