This isn’t so much to do with Microsoft’s rivalry with Apple, but rather it seems that Microsoft has yet to get around to testing their Office suite of apps on the latest macOS update, which means that there is a chance that some of the Office apps might not work properly after users update to macOS High Sierra.
According to Microsoft’s support page, “Word, Excel, PowerPoint, Outlook and Lync have not been tested on macOS 10.13 High Sierra, and no formal support for this configuration will be provided.” Note that this only seems to apply to the 2011 version of Office for Mac, so if you are running a newer version like Office 2016 then you should be fine.
However Microsoft does mention that there could be some issues, such as apps unexpectedly quitting. “Word, Excel, PowerPoint, Outlook, and OneNote will install and run on 10.13. Not all Office functionality may be available, and you may encounter stability problems where apps unexpectedly quit.”