Spending time looking into AMI (Amazon Linux), it is as usual with the plethora of Amazon products, sometimes hard to get info about what it is. I take this not as a bad thing (though it does take time) but rather a feature that emerges from the *let's develop lots of stuff all at once" product management genius. The clearest explanation of AMI in relation to other distributions was found on the SaltStack site, as:
Salt should work properly with all mainstream derivatives of Red Hat Enterprise Linux, including CentOS, Scientific Linux, Oracle Linux, and Amazon Linux. This immediately brought to mind the sense that RHEL (and CentOS) are to my knowledge never combined with these other distributions when counting them up. Counting of course does not matter, but it is important when trying to visualize linux for the Enterprise what choices are being made. Ubuntu has a lot of visibility, especially when it comes to configuring and deploying a VPS for small projects. This visibility tends to obscure the latent reality of CentOS, Oracle, Scientific, and increasing in importance, Amazon Linux. Looking at Ansible, the Red Hat deployment tool: Amazon Linux AMI is mostly compatible with CentOS, but it uses a different version approach, which means that most of those Ansible roles will ignore or complain about not supporting Amazon AMI. One can also use CentOS on Amazon AWS for a more vanilla approach, though Amazon Linux AMI is tuned especially for EC2.