Hi Kevin,
Hopefully, that has now been explained (summarised in post #871). In order to help you understand, take the platter temporarily out of the equation...
Essentially, if you dismantle an SL-1200/1210, and observe the standard bearing/chassis interface, you'll see that it is less than ideal from the perspective of optimising mechanical integrity. That is because, with no base-plate fitted, the bearing (stock or Mike New) is only being supported on three threaded 'raised dimples', which when the bearing is screwed down onto, do not allow it to make full (flush) contact with the chassis. Obviously, in that scenario, the bearing is being rather poorly supported.
It's a fundamental weak point in the design of the Technics that must be addressed in order for the T/T to perform at its maximum potential. Rest assured that without it, the MN bearing is incapable of functioning optimally. I'd say that fitting the BBP gave me almost as much of a sonic improvement as fitting the MN bearing itself, as the former simply allows the latter to perform at its maximum capability - and so the cumulative effect, sonically, of using both is superb.
The bearing base-plate Mike has designed fundamentally solves the aforementioned problem by providing a superior platform for supporting the MN bearing, thus allowing for a much more rigid coupling of the bearing to the T/T chassis. Therefore, once you grasp that fact, it's very easy to understand the efficacy of the bearing base-plate - and, as I've said, the sonic results are easily heard!
Marco.