Formal verification is a barrier to quick iteration (parent comment) not just for medical software, but anything "mission critical" where the mission is "worst case scenario, don't kill someone". Hence my point about train switching and avionics. Legal mechanisms are beside the point, I think.

As for rich constraints, that does bring up another point- how do you quickly iterate on a system full of bad data or systems of incompatible data? To get Watson to a degree of certainty, so much data manipulation and review happened by hand that it was a wasted effort.

This isn't to say that I'm in love with what I've seen of the software my doctors use (or the puckering feeling seeing how outdated the OS tends to be). I'd be a whole lot less happy, though, if their software had the reliability of say, imgur or reddit.