Why an external application instead of directly using scripting capabilities of the 3d package itself? There are advantages and inconvenient with both methods.
With an external application, .Ibl files format parsing, Collections management and database inspection are handled by that application, you write that Framework once and then you can reuse it for other 3d packages.
The bridge between sIBL_GUI and the 3d package is done through Templates that output simple loader scripts. That’s one of sIBL_GUI strength: It only took a few hours to convert the Autodesk Softimage Mental Ray Template into an Autodesk Maya Mental Ray one. Scripting a native tool with a good interface offering same functionalities as sIBL_GUI would have taken days if not weeks.
The following softwares are used to generate the Windows and Mac Os X installers:
and much more…
Additional informations about sIBL_GUI are available into this development thread: sIBL_GUI Thread