Remoak, I agree with what you are saying.
As for this:
Going back to the incident at hand, could somebody please explain why a) Air Nelson felt it necessary to re-write the checklist; and b) if the re-write was better than the original, why didn't DHC adopt it?
I don't know anything about Air Nelson but assume that, as has been alluded to here, there is some cultural thing going on. Perhaps they have a tendency to try and reinvent the wheel? As for B, it wasn't better.