while what you say is true it is not as simple as you make it to be. The textures form gsb1 are made from 3d models and thus a bump map made from them would match the lines and stuff perfectly. if you were to make a model based off of texture (and limited isometric perspectives) it would (put simply) take an exorbitant amount of effort for you to make all the little details match up which is required for the illusion to work.