I originally bought ToMI through Steam several months ago. Recently, I also got a copy from GOG.com to give to my dad. After installing it I found that the GOG version only uses 1.26 GB of hard drive space, while the Steam version uses 1.75 GB. Both versions include all five chapters.
Does anyone know the cause of this relatively substantial difference in installation sizes? Is it just the method of installation? I'd rather use the GOG version, all other things being equal, but not if it's missing anything.