Amazon is not _a_ store it is _the_ store. Once you get Amazon Prime, retail is dead to you. My personal experience (and several colleagues) of course, but once someone gets hooked on Amazon great service, 2 day shipping, easy returns, etc, you just can't use retail or even another web store. They just _suck_ in comparison.
Amazon is fantastic at what they do, more so than any other company I can think of. Maybe Apple, but Amazon is _cheaper_ than the competition not 50% more expensive.
The platform is just a bonus. They found out a way to do infrastructure right and now they are even making money on what is normally "just" a cost center.
Plus, their stock is huge because of stuff like Kindle and AWS, not because of selling books.
If Amazon had kept doing what they had been doing, Friedman would have been right.
The only place he was wrong is not realizing Amazon is a great company with the ability to foresee and adapt.