Fragmentation is a big issue on Android. A vast majority of Android powered devices around the globe are running firmware versions that have long been outdated. Android 4.4 KitKat, which was released late last year and happens to be the latest iteration, only powers a minute fraction of all devices globally. In order to curb the issue of fragmentation, Google is rumored to be leaning on OEMs to use latest version of Android in their devices, if they want them to receive access to the Google Play Store and Google Apps.
Google Forcing Android OEMs To Use Latest Version Of Android [Rumor] original content from Ubergizmo.