"Procedural Textures cannot be distorted by changing the shape of the object." Yes they can. Procedural textures, 3D or otherwise, are directly affected by the dimensions of the object unless a parametric scale option is chosen. Even then they are affect, just not distorted. So object space, world space, object cubic etc. all depend on the shape of the object. In this pic, a 3D prod texture with equal frequency settings is applied to a cube in object space, and the cube then stretched in the Y axis.