The market share bit seems pretty huge too:
By building for two years’ worth of Android (as we did originally with 4.0+), you’ll support about 40 percent of the U.S. smartphone install base. Removing 4.0-4.1 support leaves you with one year’s worth of OS compatibility, and that number drops to 12.5 percent.
By building for iOS 7 only, you’ll support 32 percent of the U.S. smartphone install base.