said by TheWiseGuy:
Can you give me any sort of motivation that they would have to deliberately hold it back if they had a version where it worked correctly (including DRM working correctly) for android devices?
Thats' just it there is no reason, unless they had some business deal with Amazon to give them exclusivity. The Kinde fire is an Android device there is no difference in developing an app for the Fire as there is for any other Android Device. So they already have the app they just are for some odd reason not releasing it.
It doesn't make sense not to release it to other Android devices, even if you put in the Android Market as is you can restrict it to certain devices with certain screen sizes if they wanted to.