But the Kindle Fire is supposed to be an appliance. It's supposed to Just Work. Adding a second tablet with a different OS would confuse Amazon's target audience.
Kindle DX has a massive screen, Kindle Keyboard has a keyboard, Kindle Touch has a touch screen, Kindle has buttons, Kindle Fire is a tablet.
And then there's the 3G and Wi-Fi splits, but that's also an obvious feature.
* Kindle (touch)
* Kindle that doesn't need wifi (touch 3G)
* Old Kindle that they need to sell off (w/ keyboard)
* Kindle w/ video + web + games (Fire)
It looks like there are quite a few Kindles, and Amazon isn't afraid to differentiate.