That field is not used, it is/was for possible future use, the file is not stored in the database, it is stored on disk under /Data/Sites/[SiteID]/webstoreproductfiles
The real name of the file is stored in the db but the file is stored on disk using a guid name and a.config extension so it cannot be accessed by an http request, but for users who are authorized the file can be downloaded by binary writing it to the response stream and will be restored to its original file name.
Hope that helps,
Joe