Thanks again, Ted.
This is what I'm posting as a sticky on the forum - but feel free to correct me since I don't have the best understanding of this:
Inkscape relies on extensions for many of the file formats it can open and save. If a required dependency is not installed on your PC then Inkscape will not load the filetype extension and the filetype will not be listed in the save or open dialogs.
If you do not have the option to save or open a particular filetype in Inkscape, check the extension-errors.log file (~/.inkscape/extension-errors.log for Linux or %userprofile%\Application Data\Inkscape\extension-errors.log for Windows) for details about what dependency was not met for the filetype.
For example, I cannot save AI files and this is was extension-errors.log says: [code]Extension "AI 8.0 Output" failed to load because a dependency was not met. Dependency: type: executable location: path string: gs[/code] This means Ghostscript (gs) is required and cannot be found. This may mean Ghostscript is not installed, or it's path is not be in the PATH environment variable.
Note that a required dependency may not be available for your platform (i.e. some dependencies might be available for Linux but not Windows). Also, if a filetype is not listed in Inkscapes save or open dialog and also not mentioned in extension-errors.log then it isn't supported.