In doing a bit of research, I've found that DirecTV does not in fact have a contract with ESPN to allow their subscribers to use this app. The likes of Wave Broadband and Walnut Communications (real companies apparently) have been able to get this done, but greedy DirecTV has not. I sincerely hope NFL Ticket someday is not a monopoly. I could have a much more useful TV subscriber if I didn't need NFL Ticket to watch the Packer games.
EDIT: Now please allow me a time of mourning as I realize I will never get to watch the game from these other angles. Without the announcers and with the camera actually on the field, you wouldn't have trouble keeping track of down and distance and would be more immersed in the game. Oh well.