The autonomic nervous system has two divisions: The sympathetic division acts to energize the body, preparing it for action. The parasympathetic division acts to calm the body, allowing it to rest. Our everyday activities are controlled by the interaction between the sympathetic and parasympathetic nervous systems.
Update: N2Aos is now available for Kindle Fire HD and Kindle Fire HD 8.9. And you get the full Android experience here, including access to the Google Play store and all the other features offered by Android 4.2 (excepting what's not available via hardware, of course).
I largely chalk that up to the more complex software running on it. Amazon's forked version of Android is likely more resource-intensive than the stripped-down, Linux-based software running on the Roku. Visually, Fire OS on the TV still looks like Fire OS on the TV.