Brian,  My first thought on this was that the sustain channel is usually
a longer slot, so if QRS were thinking in conservative terms (i.e.,
compatible with every player out there) they may have been more comfort-
able with chaining for a slot as opposed to the narrow slits in the note
field.  I forget offhand how wide the bridging is on those rolls; is it
wide enough that it might cause repetition problems on some pianos?
I bet that's what QRS was thinking back then.