Erica Sadun, writing for TUAW, compares author take-home amounts across different book formats and vendors:
As an author, you pay $0.15 per megabyte in delivery charges, in addition to the 30% off-the-top costs Amazon charges. An image-heavy book will hit you hard in the pocketbook. That’s quite different from Apple, which is happy to host resource-packed ebooks for a straight 30%.
As Sadun notes, a $9.99 ebook will net an author $5.10 via Amazon, $6.50 via Nook, $7.00 via Apple iBooks, and $9.25 via self-hosting a PDF.
Amazon’s terms certainly aren’t very generous, but authors still prefer to sell on the platform because of audience. Until the other players gain on the marketshare that Amazon enjoys, authors will continue to make the trade-off.