The Android software can be ported to a lot of different kinds of devices, including some on which third-party apps won't run properly. The Android Compatibility Definition Document (CDD) spells out the specific device configurations that will be considered compatible.
For example, though the Android source code could be ported to run on a phone that doesn't have a camera, the CDD requires that in order to be compatible, all phones must have a camera. This allows developers to rely on a consistent set of capabilities when writing their apps.
The CDD will evolve over time to reflect market realities. For instance, the 1.6 CDD only allows cell phones, but the 2.1 CDD allows devices to omit telephony hardware, allowing for non-phone devices such as tablet-style music players to be compatible. As we make these changes, we will also augment Google Play to allow developers to retain control over where their apps are available. To continue the telephony example, an app that manages SMS text messages would not be useful on a media player, so Google Play allows the developer to restrict that app exclusively to phone devices.
Posted in: Android