→Why doesn't GRAMPS just use a .gz extension?
GRAMPS uses the [http://freedesktop.org/wiki/Software/shared-mime-info Shared Mime System] defined by [http://freedesktop.org Free Desktop] project, and used by all major desktops, including KDE and GNOME. GRAMPS relies on the MIME type identified by the Shared Mime System to determine the file type of the file.
The Share Mime System allows you to identify a file's type by either using a file extension or by looking at the contents of a small section of the file. The first problem is, usually the filename or extension pattern has the higher priority compared to the contents: if the file is named <code>something.jpg</code> then it is likely to be JPEG image, not text. So if the GRAMPS XML file had added <code>.gz<code> extension to the name, the Shared Mime system would tell us that the file's type is <code>application/x-gzip</code> instead of the expected <code>application/x-gramps-xml</code>. Unfortunately, it cannot tell us that it is a gzip'd GRAMPS XML file.
The second problem is, if we looked at the contents, we would not be able to tell the difference between a gzip'd GRAMPS XML file or any other gzip'd file. If we looked at uncompressed data, we would not be able to tell the difference between a GRAMPS XML file and other XML files. So again, the Shared Mime system could not tell us that it is a gzip'd GRAMPS XML file.