I think it has to do with the way INHD wants to charge DirecTV for the channels.  INHD, which is owned by a number of cable companies, if I remember correctly, is charging per digital customer.  On cable systems the HD customers are a digital customer.  INHD is not charging cable companies for customers who don't have the digital package.  On DirecTV 100% of the customers are digital, even though only a small percentage are HD subscribers, so it costs DirecTV a lot more to offer INHD.   I believe DirecTV is in the courts now to get this changed so they are only charged for the actual number of HD subscribers and not every subscriber.