I believe that they limit the resolution for a tradeoff in the amount of HD channels they can carry. So if they increase the resolution, they have to cut back on the number of channels they will have room for. If this would be true, then we could expect the resolution to go up when they increase the amount of HD TP's. TV stations do the same thing, some offer 4 digital channels, none which are true HD quality, Fox cuts it to two of a higher quality. ABC has an awesome HD output in primetime, but they scale back during the day. PBS has several channels during the day, but at night they kick them all off, but one, and they run that one at the highest quality. All the other PBS channels refer you to their true HD presentation on the other channel.
You will all have to admit that the HD channles don't always have true HD content. PBS is one of them, but when they do have HD, they shoot it to the max, and it is usually at night.
I will be happy if Dish fixes the crappy playback on the 625 receiver I have. Joe