One of the features of NFL Sunday Ticket on DirecTV is that DirectDVR powered by Tivo (which I refuse to say as I would much rather say DirecTivo) is supposed to receive and play highlights from every game in the Showcases. This is called "HIGHLIGHTS ON DEMAND" and is true (I have learned) whether you are a NFL Ticket subscriber or not – you get the highlights either way if you have DirectDVR/DirecTivo.
Well, that would be 100% true as long as you have your DirecTivo set up with channel 582 as a "Channel I Recieve". While the highlights don't show on that channel, they are fed by the satellite to your "Showcases" via that channel. So, if you have that channel turned off (like I did) then you haven't gotten any highlights.
I turned channel 582 back on (Setup>Preferences>Channels I Receive) and – voila! – NFL Sunday Ticket highlights.