Amzn is in the build out phase for its data/fulfillment centers etc. It is better protected against competition than any other "tech" company I know of. So, comparatively astronomical PEs are going to be the norm for AMZN for a while. They can continue to grow for the next 30 years. It is not clear that any tech company can actually do that given the competition.

Once other products are good enough, apple's margins are going to shrink. Microsoft's margins are going to shrink and so will google's. That's the threat of 10 inch kindle or a kindle phone. If it is good enough, people might buy it because it can be very attractively priced because AMZN can afford very low margins. Imagine if Apple has to do with 1/2 its current margins. The stock will get crushed.