I think it makes sense for a lot of broadcasters to run a single feed.
They run HD only and downscale it for SD subscribers.
In fact, not only is it beneficial for the channel, but also for the dtho/mso as it frees up the frequency for more channels.
For example, a channel like Star plus or Sony has to produce programmes in HD. Even those boring soaps. So they can easily do away with the SD feed.
Currently Nat Geo and Discovery have different SD and HD feeds as HD is a combined feed for other Asian markets while SD is localised for India.