And here comes Google relationship with device manufacturers. As you certainly know, Market is not a part of the open-source android release, but proprietary app, that has to be licensed, if you want to distribute it on any device. So when the manufacturer licenses the app for the specific device, it also provides Google with device capabilities. Google puts it into the market, so they can show you only those apps, that your device is capable of running.
Amazon, of course, does not have such a database, and also does not have relationship with device manufacturers. It is up to them to find a way to build similar filtering mechanism. Nobody said, that building competing market is easy and that reviewing apps is enough. Good luck trying, though.
(Reading between the lines of the original blog post, possibly they just failed to enforce device restrictions for the free "App of the day" promotion.)
And even devices with the same version of Android will have differences.
