In http://en.wikipedia.org/wiki/Microsoft_Office page a little bit down until you can click on 9.1 Versions for Microsoft Windows OS and 9.2 Versions for Apple Macintosh OS. They show the 'rumors' you heard are true.
Remember the Apple already had a GUI when Microsoft only had MS-DOS. That might explain.
Why was office first released on a mac? i have heard rumors that it is first developed for a mac? !!!???