Great post Skip. That explains why you would need an A/B switch box as shown in
this diagram if you wanted to receive basic channels (2-13), expanded basic (above 13) and the broadcast HD channels without having a rented Comcast digital set top box.
But those of you with older Tivos won't be happy with this change.
However, a poster in
this thread indicates that he lost access to most of the clear QUAM HD stations after his area was upgraded.