Mac App Store version vs GOG.com version

[Mudbill]

Could it be that it's just compressed in MAS and not GOG? Does the final install take such space or is it the download?
If there are differences, it could be the editors. They only work on Windows, so maybe GOG lists the Windows size required, and that they are excluded from the MAS version altogether (similar to console versions, which are smaller than PC versions).