Errm, no suprise here
As the Fire runs a gimped version of Android that does not have the open Google marketplace, it means all content has to go through Amazon and their strict app guidelines (20k+ app downloads on Android marketplace that have no problems in Googles eyes).
This means much less content, and in particular much less FREE content, and then only the stuff that agrees with Amazon's strict policies.
I submitted my apps to Amazon, but they got rejected because they had a "my other apps" link in the app that queried for my other apps on the Google Marketplace, and frankly I couldn't be arsed to make a custom version of my apps just for Amazon and their lock-down marketplace...