Earlier quoted context omitted.
> Also, why would Amazon care so much about how others market their content, to the point of trying to interfere? They make $3 on every sale, so obviously it is in their interest to set the price to maximize revenue. Your whole bit about "everyone doing it" and "race to the bottom" is an instance of the zero-sum fallacy.
And your evidence that this isn't a zero-sum game, is, exactly, what? All of the evidence points to the fact that people have more than sufficient entertainment options and have set their budgets at a fixed point. It wasn't piracy that killed music. It was the fact that the prime purchasers of music had a fixed entertainment budget and switched to buying video games aka. zero-sum market.
Another issue is that some recreational products are rivalrous of time; you can't read a book and play a computer game simultaneously, or combine one of those with doing the ironing or cooking dinner. You can watch a video or listen to music while you're doing something else. Oh, and some products are use-once, while others are use-many-times (and in some cases this varies from individual to individual: do you re-read books, or read them once and discard?).
TL:DR; There's a zero-sum game in the picture but nailing it down is a whole lot more complicated than it looks at first sight.