are all HD programs filmed in HD, or are some older shows which were originally shot in SD just upscaled by the networks and then just broadcasted in HD? just curious because i guess that would explain why some HD shows look much better then others. Is that why DiscoveryHD looks so better then other HD channels?

Also, is SD considered 480i or 480p?

I think its 480i, but is it possible that some SD channels like HBO (not HBO HD) are broadcasted in 480p?