So they force him to use Word hmm?
I doubt publishers *demand* Word. It may be some use it as their defacto interchange format but I expect most authors with a relationship with a publisher could ask to use another format assuming it fitted the process, e.g. ODT.
At worst it means doing a bit of importing / exporting to get a file to them in the format they want. It doesn't mean the author has to use the tool day in and day out. The bulk of the book could be written any way they please. Even in a .txt file.
I expect the main use of Word is when a manuscript is submitted and has to go through some rounds of editing - to pin notes on sections, revise paragraphs and so on. It's hard to see how some advanced word processor is avoidable at that stage unless they want to go back to the old process of scribbling over a printed manuscript in red ink.