DB6,
I believe that this change came about because of the night when a fair few aircraft landed at STN below minima. This scenario is easier to administer when (like the STN incident), the minima is dictated by downgraded ground facilities.
I'm not sure if a Cat 1 aircraft's flightplans would show this, but our filed flightplans (Cat3b aircraft) show our minimum RVR of being 75m