derefr cited one reason but there's another that's relevant to this thread: updates. In the Android model handset manufacturers and carriers decide when (or if)

derefr cited one reason but there's another that's relevant to this thread: updates. In the Android model handset manufacturers and carriers decide when (or if) to ship updates. Google distributing their apps through the store gives them a way to roll out new features to a reasonable portion of their user base.