Most models are created by humans and humans have the freedom to model how they want or how it is convenient for them. There are two "standards" relevant for this, the technical one is how SketchUp creates Collada files (Collada specification) and the other is a proposition for modelers to follow, the Google Earth Acceptance criteria.

If you don't like to have interior  faces, group the model and choose Tools → Solid Tools → Outer Shell.