I don't like the idea of airing different things on HD & SD versions of the channel. Both are supposed to be the same channel, just different quality. So both should air the same thing. Airing different things on channels with same name makes no sense. Also, what if I have subscibed to the HD version, but one of my favorite movie is airing on the SD channel (or vice versa). That means I have to subscribe to both channels to make sure I don't miss anything.
Let's take a channel called "XYZ Cinema". If they want to launch a new HD channel and not air the same thing, then they should name the new channel as "XYZ Cinema 2" and make it an HD-only channel (or Ad-Free too) instead of launching it as "XYZ Cinema HD". If both have different names, then it makes perfect sense if they air different things at the same time.