If this was only about a cost per subscriber, I would agree with you. But if the article posted earlier is correct, ATT wants Dish to guarantee a minimum number of subscribers. Let's say that minimum is 2M. But only 1.5M sign up. Dish would still have to pay ATT for the other .5M. Couple that with a (presumed) rate increase, and I don't think it's ethical bargaining (note, I didn't say illegal).
Now, I guess there could be a "fair" way to do the guarantee. In that, you have different levels and the more subscribers you are willing to guarantee, the less per person the cost is. So if Dish is willing to guarantee .5M, then ATT gets $10/subscriber. If they guarantee 1M, ATT gets $9/each. 2M is $7/each. If Dish isn't willing to guarantee any, the charge is $12. Obviously, I made the numbers up, but I don't think that's an unreasonable negotiation tactic.