I think what bezos does, is asking: in the e-commerce business, what are the difficult parts and the parts that change less often and how do we make sure that we are the best in every one of them?
This is the reason bezos thinks long term. because he can.
Some of those parts are:customer trust,the need for computing,fulfillment,delivery,payments and access to targeted eyeballs,all content will be digital, need for marketers(affiliates).
Serving as a leading infrastructure platform is a great way to achieve this.It gives you revenues , it puts you under customer pressure and i think the new market dynamics works better for amazon also as an integrated retailer, by letting amazon control prices and service levels and limiting the platform, by decreasing competition to a small number of companies in the industry and by pulling startups towards them.
Now combine the (small?)benefit of each platform gives you over competitors, together, and you got a big competitive advantage.
On the other hand, having a great platform let's you profit and learn from the things that change fast.