A high degree of fragmentation is a problem that Android app developers have had to deal with since day one. Next to the fact that Android devices come in an endless variety of screen sizes and processing power, developers are also facing a high degree of software fragmentation. Many device manufacturers superimpose their own user interface on top of Android (think Samsung's TouchWiz), often making it impossible for users to get future Android updates. As a results, adoption of the latest version of Android has traditionally been slow.
KitKat, the latest iteration of Google's dessert-themed Android updates was supposed to change that. It was designed to be more compatible with low-end devices in order to get it to more devices quicker. Thus far, it doesn't seem to have worked though: according to Mixpanel less than 10% of Android devices are currently running KitKat, which was released in October 2013. By contrast, iOS 7, released in late September has been adopted by 85% of iOS users and even iOS 7.1, released as late as March, has a significantly higher adoption rate (42.77%) than Android KitKat.
The Statistics Portal
Statistics and Studies from more than 18,000 Sources
ProductsAdvertising on Statista (PDF)