The first Kindle came out ~3 years before the iPad. In a parallel universe, the new Kindle Fire is still the Kindle tablet we'd be getting now if Apple hadn't ever made the iPad at all. That's a huge difference compared to everybody else who are just making iPad copies.
It's interesting that Apple and Amazon both started with simple devices for specific types of media, books and music, and grew out to encompass the rest.
I almost feel sorry for all the other Android tablet companies, who's going to buy one now, knowing the Fire is coming?