When you look at the cell phone market, there is a about the same percentage. Overall between cell phones and tablets, Apple only owns about 25%-30% off the market. Android has a major advantage as there is more then one manufacture, ie. Samsung, Nokia, Sony, etc. At the present time the Android market is much larger then iOS, this is mainly due to affordability. It also shows that the Android(Google store) has more apps, more support, and is making more money.
I have all this as I am currently working on a major mobile application project for a large world wide corporation. The only really difference in markets is Europe where the Microsoft phone holds about 10% of the market, which cuts into the Android market share as opposed to the Apple.
Market research is showing that making an app available on Android is more beneficial as it will reach a larger market share. The only statistic Apple has going for themselves is customer loyalty. Apple customers will continue to buy Apple products.