You're missing one point - if tablets become commoditized, Apple still wins because they're establishing ownership of the ecosystem today.
You're spot on identifying Amazon as Apple's only real competitor.
You're spot on identifying Amazon as Apple's only real competitor.
Amazon was, however nowadays Google sells music, rents and sells movies, sells books, and of course sells apps. The reason they rebranded the Android market to Google Play is because of this ecosystem.
So - my counter point would be that Google will be a competitor in time.