Fragmentation isn't always a "problem." In many ways, it offers users and developers a chance to experience great choice and variety.
The proliferation of devices with their associated screen sizes, internal hardware and custom ROMs creates some difficulties, though, as when a particular app doesn't work at all, or works poorly, on particular devices and operating system versions.
OpenSignalMaps, for example, has identified 681,900 of discrete Android devices, and looked at models, brands, API levels (the version of Android) and screen sizes. And yes, you could say there is a great deal of fragmentation.