Over the weekend an MS exec took a poke at Apple by tweeting that Microsoft doesn't take 30% of the profit you might earn from content you create in Word, Excel or Powerpoint. But iBooks Author is a different beast. It's not a generic document creation tool. It's a publishing tool specifically designed by the publisher (in this case Apple) to format documentation for their platform. Many other publishers use similar proprietary tools that generate content in the format(s) they require in order to publish your work.
Here's a better summary: [dimsumthinking.com]