I doubt Apple are worried.
Amazon's track record in the consumer space - with mobile devices in particular, is spotty at best. They're good as purveyors of content and other merchandise, but they aren't a mover and shaker on the level of Apple and I dare say Samsung.
Once Apple introduces a serious contender in this space (TV plans, etc), Amazon and the others will be relegated to the level of an afterthought.
This all depends on whether Apple treats this space as an...