I am not going to dispute the SD TV longevity. However, virtually all over-the-air stations now must broadcast in digital which requires a digital conversion box. All televisions purchased today are HD. We have two HD TVs and two old SD TVs with digital converter boxes.
It is not only Dish who is inconsistent with HD/SD. Some local stations broadcast the SD signal in a letterbox format. On an SD television, there are black bars at the top and bottom. On an HD television, there are black bars on all four sides. Other stations broadcast the SD signal in a way that the left and right sides of the image are cut off. I still cannot figure out why some stations broadcast an SD signal when they claim to be HD. For example, our local PBS station will broadcast The This Old House Hour in HD on Thursday night on 39.1. Saturday morning, they split the hour into This Old House and Ask This Old House which are broadcast in SD on 39.1.
Our local Fox station broadcasts in 720p, but Dish gives us the SD version with the left/right sides cut off. Usually not a problem except when you are watching a baseball or football game and you can only read half the score.
I know bandwidth is an issue, but all other things being equal, it would make more sense to me for all stations to be broadcast in letterbox form. SD signals would have black bars at the top and bottom. Those with HD TV could zoom in on the SD image. HD broadcasts would fill the screen.