In fact I'm not much into understanding business, and Amazon is my soul pet, cause it's a great opportunity for me in a country of a third world to get all the wonderful things I want to have. Despite the fact that delivery to my country is expensive and I have to wait about a month or so - it's fantastic.
In all the other cases I use local shops, if what I need can be found there. So in my opinion it's just an international option, but not small business killer anyway.