Dish's National PBS feeds have been SD for forever. Local PBS stations may be HD, but I don't have one in my DMA. Fortunately, PBS streams in HD which, with the right URL, can be recorded.
I have the Jade TVB International package and on some channels, there are SD and HD versions, I prefer the SD versions when recording to the DVR as it allows me to record more. Some have streaming version of the channel as well.
PBS itself transmits the national feeds of its SD channels (Create, World, and First Nations Experience) in widescreen. With adequate bandwidth to make them look good, of course.
I watch the NASA channel a lot, there's tons of great stuff on there and you're not beset with garbage ads all the time. It does look lousy though. I have their app on my phone and can watch it there in HD, but it's not the same as a TV. International channels look terrible too.