I have an aquaintance at ESPN and he explained to me that HD is so much more expensive because everything in the chain has to be HD quality. Cameras, trucks, all the uplinks to the satellite and downlinks. I had asked him because the only Indy car race in HD is the Indy 500 but none of the other races in the series are. He told me if it doesn't have the ratings it won't be in HD simply because it takes a big chunk of money to broadcast.
So maybe the cameras are HD capable but are the CTN trucks and all the other equiment?? Anyway, I'm just repeating what my friend told me so if I heard him wrong someone in the know can correct me.