What you're missing is that, from the author's point of view, ebooks are not interchangeable. A unit of my sales is not usefully interchangeable with a unit of Scalzi's. To Amazon we're fungible produce, but to us we're suppliers of bespoke one-of-a-kind products. The Amazon move squeezes those of us who are able to sell at a higher price point -- like me (current lead title priced at $12.99 on Amazon and selling jolly well; and at £7.99 in the UK, and doing well there, too).
Amazon's proposed $9.99 guillotine on pricing would basically impose a 30% cut in my income if sales volume of my titles remains static. And I haven't seen any evidence that the price elasticity of demand for novels by Charles Stross will respond to crude pricing signals the way that aggregate demands for all books will do across the board.
