When you refer the the "large install base" associated with Canonical, I assume you mean Ubuntu on servers. Lots of people do run Ubuntu on AWS, but Amazon never needed to own Canonical to make that possible.
The Kindle Fire OS is a fork of the Android Open Source Project, not Ubuntu or Ubuntu Touch.
The differences are not large, but your institutional knowledge, existing management scripts/tools, custom packages, and (presumed) working relationship with Redhat the company all contribute to making one wonder whether it is worth it to switch hundreds of thousands of servers (millions?) to another distro. You could, but at what cost for what gain? Why, upgrades are trouble enough.
The Kindle Fire OS is a fork of the Android Open Source Project, not Ubuntu or Ubuntu Touch.