In actual use we might get a situation more like HAL in the movie 2001, where they added special secret programming in the last minute:
"HAL, the symptoms are difficulty breathing and wheezing when subject is under stress."
HAL secret programming:
possibility 1: has a cold virus
possibility 2: has asthma
cost to treat #1: $25
cost to treat #2:
Further testing required: $1000
If asthma detected, $2000+/year
"Patient has a cold. Recommend decongestant."
Given the algorithms they developed, I would trust Watson much more than the average doctor to correctly assess my medical condition. Once tapped into the medical knowledge base, I could easily see a Watson connection in every doctors office so they could feed in the inital data and then get a list of useful tests to run to clarify the dianoses and prescribe the correct treatment.
I hope the AMA embraces the capability that Watson could offer to the public in more accurate medical treatment anywhere in the world.
Just a thought.