what do you mean by "beard".

Bearding = migration of fibres from the batting that pass through the quilt top or backing to form a fuzz on the surface of the quilt

Regarding the cheesecloth, I think it is an interaction process. Wool fibers, unlike cotton, have tiny barbs on them. This is what causes wool to "felt" -- the barbs interlock tightly with each other, so tightly that felted wool does not ravel when cut. With the old style wool battings, I think the cheesecloth provided a type of scrim. The barbs on the wool fibers could grab onto the cheesecloth, providing a surface for other barbs to grab onto. The cheesecloth wasn't so much providing a barrier as it was providing a scaffold for the wool fibers to lock onto. My theory, anyway......

True or not ... your theory makes total sense to me, Prism! :)