→Why doesn't GRAMPS just use a .gz extension?
For these reasons, we must rely on the <code>.gramps</code> extension. If we don't, we would not be able to tell if this was a valid file. Even worse, the mime type of <code>application/x-gzip</code> would be associated with another application (such as File Roller or Ark) instead of GRAMPS. The mime type of <code>application/xml</code> may be associated with XML editors (Bluefish, Conglomerate, Emacs, etc). In that situation, the user double-clicking on the file in the file manager (or performing the default action for the type by any other means) will never launch GRAMPS with this data,
GRAMPS is not unique in this problem. For example, the OpenDocument format used by OpenOffice, KWord and AbiWord is actually a collection of files in a <code>zip</code> archive. If you run <code>unzip</code> on a OpenDocument file, you will see something like:
$ unzip test.odt