If I recall correctly the NFL network is tied to carriage of the NFL Sunday Ticket package, currently only available on DirecTV. IMHO that is likely to remain the case for the forseeable future as Charlie is never going to offer as much for it as the NFL can extort out of DirecTV. We will probably never see it on Dish Network for that reason.
NFL Network is, in no way, tied to the carriage of NFL Sunday Ticket. It's a seperate channel that is available to ALL companies who are interested in adding it. Several cable companies have announced carriage of the NFL Network without Sunday Ticket.