The only download mechanism currently provided downloads a .diff file that attempts to show the differences in files. For Word and/or Excel files, that are much less likely to be included in a ...
Unless I am misunderstanding what you are looking for, you are in luck - there are two places you can download a copy of the files - in the review summary screen, in the review materials section, click Download -> Files to get a ZIP file of (I believe) the latest uploaded versions of all the files.
If you want to download a specific version of a file, in the diff viewer at the top where you select the version to display, there is a download icon which will let you download the displayed version of the file.