Well, the problem is that Amazon doesn't have all the experience Apple has.
Why do you think there is a 15 minute timeout now? (iOS4)
Why do you think the 15 minute timeout is split between IAP and regular app store purchases (iOS5)?
Why do you think apps now have clearer markings on IAPs (iOS7)?
Apple ran into this, then implemented the safeguards - the 15 minute timeout because kids were clicking "buy now" without realizing it and running up thousand-dollar bills.
The split because mommy/daddy would get the app, and within 15 minutes the first IAP would pop up and the kid would run up charges.
The clearer text because the FTC, after seeing Apple settle the class action, decided Apple didn't do enough and fined Apple for what the FTC felt was more "sufficient" damages. (Apple did not contest this because of the legal costs).
Sorry, but for me to feel Amazon any sympathy, I feel they all should have the same restrictions.
As for banning IAPs? Well, the rise of IAPs and all that helped produce alternative business models for games, and created innovation (as well as exploitation, such is the world).
Stuff like free-to-play, ad-supported, etc., helps combat piracy (rampant in the Android and PC works) and revitalize those markets. The PC world was headed to an online-only world where the online component was the DRM part, and now we have it where it doesn't matter if you pirate anymore (because pirates can't do IAPs and can be put in a disadvantage).