Scarred but understanding now I'm an author too
I wrote "Getting Started with LevelDB" last year, for Packt. They too insist on using MS Word for two reasons. One is the collaborative markup with commenting and change control. The other is a strong style-based production pipeline.
They produce cheap 120 page, highly-focused books and have a production process that requires the author to use an exact range of MS Word styles that then map directly into their production styles (presumably using InDesign or similar).
The collaborative markup was both a blessing and a curse.
Some chapters went through 5 revisions with the technical editor (trying to write about Objective-C in 4.5 pages per chapter with multi-line wrapped source examples is a nightmare).
You need a way to have comments attached to specific points in the text, with anchoring that will survive editing by more than one party.
That is a non-trivial exercise, far more complex than any stylistic markup.
I would love to see an extension to Markdown which coped with editing markup or maybe a tool integrating Markdown with version control that offered at least the functionality of MS Word's commenting, for non-technical users.
I am NOT a fan of Word and the bubble comments don't scale - beyond two participants and multiple reviews they become a confusing morass. I would be very happy to hear that there's a better alternative.