You only have 2^10000 if you have bad boundaries and overcoupling of your subsystems. Thus another benefit of unit testing is validating your architecture: bad architectures are inherently difficult to unit test.
This is true, but the interaction between the doctor and the nurse was invaluable. The context of those orders and the nurse's knowledge of the patient were used to come up with a plan together. Reducing that interaction to "order giver" and "order taker" greatly reduces the quality of patient care. I was recently in the hospital for a week and this was an issue several times.