That's a problem, yes, but it's not a new one. Vendor management has been around for decades, centuries, millennia maybe. If I contract out part of my job, it's still my responsibility to make sure the contractors are doing their job right. "But their marketing said..." or "but their sales guys said..." is not an excuse and everyone knows that.
Doctors noticing that Watson is wrong is expected. Doctors missing the fact that Waston is wrong is a failure of that doctor and the doctor who didn't check the results is the responsible party. The checks don't come from Watson, the checks come from humans who oversee Watson.
If Watson is wrong often enough that it's hindering the doctors, then kicking it out is the right call. But there can never be an argument of "Watson got the diagnosis wrong and that's why the patient died" because ultimately IBM is still just a vendor and Watson is still just a contractor.