On the topic - Oblivion/NWN/Baldur's Gate load in the interior of houses as different levels. Gothic doesn't. Both methods have advantages and disadvantages - which do you prefer ?
To save performance, I would say the Baldur's Gate method is the better one. As you said, Oblivion does the same. So you can design very highpoly house environments without having the whole world loading in the background. Gothic's houses look imho very low detailed and don't have so many things to manipulate. And all things are "stuck", not much options to move/interact with them.