There are different ways to communicate an idea. When you visually communicate, you can use conceptual, graphical, physical and CAD based development. And these can be taken forward both manually and through machines. Each comes with its advantages and disadvantages, and must be understood as a whole.
 
My take on the IB Curriculum Structure:
If you see the IB curriculum, you will find that the way I have put together the chapters, they differ in order. This is because this is the best way (I feel) to teach Design Technology. Starting from how one comes by ideas, develops them, manufactures them, keeping comfort a priority, and manages resources to come up with a great design solution.