[robbiemitchell]

It seems Amazon is effectively the entire market: customers, distribution, payment.

If Amazon were worth only 10%, it would be irrelevant and publishers would go elsewhere.

If the combined value to an author of a publisher and Amazon were only 30%, they wouldn't rely on either so heavily. But here we are.

[rtpg]

I think this is one of those points where a lot of people on HN will think in terms of COGS, but because Amazon is effectively offering your products at such a large market, the 70% of revenue you'll get through amazon is worth a lot more than the 100% you'd get without going through them (and by definition, more than the 30% they're getting).