Interestingly the distributor has come up with the following.

Because round core strings don’t have such a tight grip, in some circumstances the tension holding the core and the wrap wire can get lost and these two parts become slightly detached from one another.   Tonally, this results in the string sounding ‘dead’ which is unfortunately irreversible and therefore a new string will certainly be needed. This can often happen when the strings are trimmed prior to them being fitted to an instrument (more on this below).

We mentioned earlier that many string makers have made the switch to using hex core strings and Chas pointed out that “this shift was nothing to do with tonality differences. It was all about making strings cheaper to manufacture and reduced the likelihood of a dud string getting through quality control.”

Doesn't stop them from charging £25 though. Take your point about esoteric guitars etc. I'm currently having an interesting discussion with the distributor's M.D.. He has come out with some real howlers. Watch this space!