Oops,
Or I could have the file-storage-dav package create a callback on the file-storage package. This way it would only exist when file-storage-dav is installed. This seems cleaner from a maintainence point.
The reason there is a file-storage-dav package is that there are some content_type specific operations that are needed for file storage objects. If the default content_folder/content_revision WebDAV operations were sufficient, no additional code would be needed.