I'd say this particular issue is a non-starter, considering that no other provider offers a receiver like Dish does that drives 2 TVs (SD or HD)... Unless and until a competitor offers a receiver that can output to two HD TVs with unique channel-viewing experiences, Dish has nothing to worry about in this particular area.
I get asked about this all the time by current Dish customers who are disappointed with the SD picture on their new HDTV, especially after having gotten used to HD on their main TVs. Then they call Dish, and are often upset to find out what it will cost them to get HD on 3 or 4 TVs. The next step is looking at the competition for a better solution.
It may not be such a big deal for new Dish customers, but it's a big deal for retention, at least in my area.