I have noticed it as well on my 622. Mpeg2 looks better to me. My HD locals from E* also experience similar problems, NBC being the worst. I just barely switched from D* where I had CBS & FOX from L.A.. Thoses channels looked much better than anything I have seen in Mpeg4. I hope they fix it soon.
So far all of the HD channels (excluding the HBO, SHOWTIME, STARZ) have been available to all HD metal packages (bronze, silver, gold ect.) I don't think that they would start now with making customers upgrade to gold just to get NatGeog HD.
On their website they have the SD NATIONAL GEOGRAPHIC listed on the DishHD Gold and higher. The HD verision of NATIONAL GEOGRAPHIC is listed on all packages. Hopefully that indicates that all HD subs will get it.