Yes, the H series receivers are fully backward compatible to SD programming. The HD receiver can receive SD but an SD receiver cannot receive HD.
WHEN/IF DTV drops SD broadcast from the 101 satellite they "should" broadcast some amount of programming in HD from 101. With the H series receiver you would suddenly be able to watch DTV with a dome in HD! The only question is what channels will be available. DTV previously listed a small number of channels that would be available but, to my knowledge, no one has a complete list. NO NETWORKS is almost a certainty but the rest remains a big question mark.