I would suggest that the vast, vast majority of companies that use Windows do so for two reasons
1: Because the software is (mostly) interchangeable with what their customers use. Office docs can be opened in any Office application without any formatting errors. Generally speaking. Open an .odt in Word and it could (will probably) end up buggering up the formatting.
2: Because most business owners don't want to go to the expense of hiring a dedicated IT guy to manage a bunch of computers that their staff don't know how to operate.