Mac Office is not the same as Windows Office.
It lacks the extended functionality (i.e. in Excel: PowerQuery/Pivot/Map, Inquiry) or for some reason doesn't work (Mac Excel does not work with psqlODBC - Windows Excel does).
Not in the world I'm living in.
Windows-only software is far, far more common than Windows+Mac software.
(The software I'm talking about is Windows-only. I know you might mean Mac Office.)
PS: And because writing portable software, deploying and maintaining it is apparently hard, companies are now switching to web-based solutions. Yay :(
Edit: Well, the edit just done to the parent comment makes my comment mostly useless now. :P At the very least, speaking to the specific example of Word documents, I’m not aware of any features that current Windows Word has that Mac Word doesn’t (that would result formatting not carrying over perfectly).