People have been beating Apple on price for years, yet Apple are still here and still reaping their profits. These are not commodity products - I doubt that too many people would choose a Samsung tablet over an Apple one based solely on the fact that they were £100 cheaper. If I want an iPhone or an iPad, I'm only going to be buying it from Apple
Amazon, on the other hand, offer pretty much nothing that couldn't be copied or beaten by a big retailer (someone like WalMart, or Tesco in the UK) if they really put their mind to it.