Bezos wouldn't need to "turn the WaPo into Amazon's personal PR factory" in order to get this published though. You don't have to have a massive conspiracy to get a story published. Everyone in PR knows that.

All he'd have to do is mention the research to a few writers. If you're a writer and the owner of the company mentions a story that sounds interesting to you, you might be just a little etra inclined to cover it.

The first season of House of Cards is a nice illustration of how the combination of powerful people and ambitous writers can lead to a "journalistic" PR campaign without any mass conspiracy. Granted, it's fictional. But it's a plausible mechanism.