I came upon this article which outlines the capabilities of the different readers: http://ebookarchitects.com/learn-about-ebooks/enhanced-ebooks/
The key chart for this topic:
I can tell you that the moment one of these other platforms develops a packaging system for deploying HTML/CSS/JS animations we'll dig right in!
One promising tool is the Kindle Textbook creator in Beta: http://j.mp/1UdV6K7. The tool is meant for audio/video & mathematic equations, and seems built around the conversion from PDF --> Kindle Format (.mobi).
If Amazon were to support the .wdgt package in some form, they'd make a lot of people very happy.
Once when I said 'HTML only works on iBooks', I was quickly corrected and sent a link to Readium. For schools that deploy Chromebooks, this is a good tool for reading books.