Actually, there is a good chance that this is temporary.
I imagine they took some base stable version of android, and built their services platform on top of that. They have their own ridiculously huge Web Services platform that they want to provide that at a system service level to application developers.
To do this quickly, they had to throw out a lot of hardware support both at the system level for things like gyros, hardware buttons, GPS, etc (all the things the iPad and Google Tablets have), to be able to undercut the manufacturing price to an attractive retail market value.
There is a good chance their video streaming leverages system services built off an increasingly "Amazon" branch of early stripped down Android code.
Once they have their platform, they can focus on rolling back in the hardware and services to support a larger eco-system.
Ultimately, I think they are trying to enable a hub to provide all of their web technology through a mobile device. They've chosen android to safe themselves a lot of time plus they aren't OS guys.
Now they are the awkward cousin that doesn't have a fully realized value proposition and is semi-cross functional with other devices and more enhanced platform.
In fact, developing for Kindle Fire would probably feel a lot like porting an Android app (that was originally written for iOS in Objective C) and designing around the current hardware peripheral limitations (and the fact that "Google" intents would be completely ignored).
What they could be betting on is the shear technical force of their infrastructure and web services. If they can bring high-quality content to their users consistently, people will feel the comfort of Amazon more than other eco-systems.
This puts Amazon in a weird position because they are competing with Google more than Apple, really. Especially since they chose Android. Google expected making and distributing Android would increase the gravity to their platform, but its totally possible they understimated Jeff Bezos and his ability to leverage it.