Originally posted by Ebyl:

The game uses a very simple concept of distance from the ground (number of connections) as the main factor in stability. Cross beams and other normal supports don't add to stability unless they lessen the number of connections to a grounded component.

Who knows, maybe they'll add a more complex system in later.

I think this is conpletely an unnecessary concept if you want the game to contain a feature of building speciality there should not be any limitation except actual physical rules.