Strange... I was able to enable third-party sources and install APKs from the web with no issues on my Kindle Fire HD. I don't think that it would be impossible to install an appstore on one.

That doesn't make sense. How are they going to prevent you from installing a store APK?

That isn't entirely accurate. The Fire doesn't prevent you from installing arbitrary third party apps and app stores. It's just that it can't use the most important one: Google Play.

This is not entirely the Fire's fault. Play is no mere standalone app; it needs some hooks built into the OS itself. Installing it on the Fire is possible, but involves deeper magic than even the average developer can be expected to know.

You can blame Amazon for not including that support (and I do), but you can also blame Google for requiring it (and I do).

> bare ipa installation

You mean APK?

Since you can install a 3rd-party app store on Android simply using an APK (e.g. Amazon Appstore on non-Kindle devices), I don't see how Amazon could allow apps but not app stores.