Exported a page to Word, and this is at the top of the resulting HTML file (when opened in a text editor):
The file is not a valid Word document, in fact it rather seems to be a .eml file. It is basically coincidental that Microsoft Word can open the file. A major problem with even this is that *file:///C:/* prefix is added to each content element (images, etc), regardless to the operating system/browser that you use it for export. This path is not even valid on most Windows machines for such exports.
A work around exists - export the page as a PDF, and convert the PDF to Microsoft Word Format: