If the writers take advantage of Amazon’s new “70% royalty plan”, they’ll make a much bigger slug of that $10 than they do of the $15. And if and when the publishing industry finally begins to understand the price/volume trade off and Amazon sells the same books for $4.99, the writers will sell a even more of them and do just fine (especially if the publishers’ share is squeezed).
Also, please don’t argue that, if Macmillan goes bust, books will be bad. Publisher editors don’t really edit books anymore. They acquire, package, and market them. And that’s fine: Everyone’s strapped for time and money these days, and editors just don’t have the time or money to edit anymore. (But books are still fine. In part because many writers hire freelance editors themselves.)
Yes, if Amazon charges $9.99 for ebooks and “prints” them instantly, some writers will conclude that they don’t have to write 100,000 words and wait a year for the publishing industry’s dinosauric practices to finally get the thing into physical print…and they’ll write shorter, more timely books that will skip the whole “hardcover” process altogether. But, again, that’s Macmillan’s problem, not ours.