The Ziggo dreambox channel list page is update so that you now can choose between a channel list that contains both the SD and HD channels. This is handy for non HD receivers which cannot handle the HD stream.
And there is an option to replace the SD channel with the HD version. This means that you will need a HD capable receiver. The idea is that you don't need channels twice in the list. If you have a HD receiver and HD channels, you don't need the SD channels.
For more information go to the Dreambox Ziggo Channels project page.