Horace Dediu with an excellent analysis of the competitive threat Amazon poses to Apple:
The assumption (implicit) in Kindle is that the product is “good enough” as it is and should be used for many years to come. That’s not a way to ensure improvements necessary to disrupt the computing world.
I hadn’t thought about this, but Amazon makes more money if they don’t sell you next year’s model Kindle. That is, they introduce new Kindles just to try and gain new buyers. Apple introduces new models to get upgrades and new buyers because Apple makes more money on the hardware sales themselves.
Also see Dediu’s note about the Apple TV.