My parents had extended basic. My father's understanding was that Comcast's mandate that they switch to a free, deck-of-cards sized set top box, and/or rent a Comcast DVR, meant in part that the digital signals being delivered are switched. Perhaps that's switched for smaller viewer share, and multicast for those channels with heavy viewership -- that's what I understand you to be saying.
This week's been my week to repeatedly reveal myself for the fool I am. So, I might as well make a thorough job of it in this thread.
P.S. As I recall, his thinking was in part that to keep the "deck of cards" transceiver small, power efficient, and cost effective enough, it must be receiving a single switched signal rather than trying to handle multiple signals. But perhaps it is picking amongst multiple signals, but only handling one of then at a time. (So, e.g. not producing multiple outputs that would enable a old Tivo to keep working.)
Sorry if this subthread is going on too long.
P.S. Thanks again for the explanations/clarifications.