It is based on the failed assumption that the only waste that matters is manufacturing waste. Can you imagine a manufacturing process that produces a defect and there is no one in the organization to work it with the customer? At every stage of the value stream it is possible to have defects. If the process is not mistake proofed then the need arises to have a support organization that fixes the problem while manufacturing still focuses on delivering value. It is too obvious to say that any organization that does not have to produce value can be of great value to the customer and the organization. As Ohno said, go to where the organization is hurting. Applying lean to only manufacturing may be short sighted.
Having trouble knowing where to start, or go next, in your lean transformation? The Calibrate Lean Assessment can help you understand your transformation program's biggest weaknesses. Check it out.