Amazon relies on insane volume to make up for insanely low margin. They are just one administration away from investigation for anti-competitive pricing where they sell at break even or loss to undercut brick and mortar. Not saying it will happen, but there could be a regulatory pushback someday in the future depending on how their online model warps economies and how much of it they dominate. I think their biggest threat is from a paranoid regulatory response some time in the future. But they also have their hands in cloud services and other technologies, so it's actually more complicated than that. Amazon has demonstrated an amazing capacity for transformation when you look at what they started out as. Pretty impressive.Amazon -> ??? (I can't think of a very relevant comparison)