FWIW, I don't think any publisher that uses an actual printing press uses Word to typeset books, simply because they almost certainly use the whole Adobe toolchain for prepress [1], and InDesign integrates much more nicely with this process. For example, Word has no facilities for color spaces, separation, or generating the actual plate images.
I guess they could generate PDFs from Word files with Acrobat and shoehorn them into the process, but any publisher that is actually satisfied with doing that is bonkers.