One of the most useful techniques for growing a videogame user base is the addition of modeling capability. We have seen games like Skyrim play far beyond the normal lifespan of a video game because of their extensive modeling community, something embraced by their developers.
Allowing simple modification to textures, models and other components allows users to change the game to suit their taste, add new content and expand upon the existing game.
Making a game modifiable need not be hard. While it is wonderful if developers provide tools for doing this, the simple act of making game resources (e.g. image files, sound files) available and not compressed into exotic formats which are not easy to access, still provides the ability for modeling.