My theory as to Amazon's valuation is that investors assume at some point Amazon will get a stranglehold on retail (giving it both monopoly and monopsony positions in many markets) and then extract rents on a staggering scale until regulators eventually deal with it (which might be never).

But Amazon's experiments with treating workers as commodity parts in a machine -- which we discover also applies to the white-collar folks (so now we care?) -- is a whole other angle. Instead of merely planning to cash in on a prospective illegal monopoly, it's also working on making life miserable for all workers. So there's that too.