Bagheera,
I understand what you mean Scuzi and I dont wish to denegrate the need for precision its just that in 15 years of experience I have never come across such a situation. More importantly I have never heard of an incident where this was involved (I stand to be corrected). It appears to be an apochryphal tale.
Then I guess you've never worked at an airfield that has numerous flights by airlines from the States in to it.
A brief survey of one, me, suggests saying milibars at such airfields is actually quite important given the number of times over the years the QNH has been read back to me apparently as inches rather than milibars.
I'm all for it.