The short answer is that Android/Kindle/Nook are different platforms. Thank lawyers and Android fragmentation for that.
True ‘Android’ (copyrighted trademark owned by Google) must be licensed by Google. Amazon and Barnes & Noble have rejected Google’s terms, refused to pay Google’s licensing fees, and have forked off the main source code base. Not all the stuff that ships with Android (™) “proper” is open source and allowed to be distributed. Google Play and Maps are off limits to non-licensees. This means these portions of the code base cannot be compiled in/shared for Amazon/Nook apps (at the risk of lawyers getting involved) so each platform has to have completely different implementations for this stuff. (Nook and Kindle are competitors too so they don’t share anything either.) This is why we have to have different build targets that are all slightly different from each other.
One reference:
http://source.android.com/faqs.html
(A couple of highlights:)
What does “compatibility” mean?
We define an “Android compatible” device as one that can run any application written by third-party developers using the Android SDK and NDK. We use this as a filter to separate devices that can participate in the Android app ecosystem, and those that cannot. Devices that are properly compatible can seek approval to use the Android trademark. Devices that are not compatible are merely derived from the Android source code and may not use the Android trademark.
What is the role of Google Play in compatibility?
Devices that are Android compatible may seek to license the Google Play client software. This allows them to become part of the Android app ecosystem, by allowing users to download developers’ apps from a catalog shared by all compatible devices. This option isn’t available to devices that aren’t compatible.
How can I get access to the Google apps for Android, such as Maps?
The Google apps for Android, such as YouTube, Google Maps and Navigation, Gmail, and so on are Google properties that are not part of Android, and are licensed separately
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