Phil, you can indeed subscribe to a digital only version of Sky & Telescope (US edition) for $US15 for 6 months. See
http://www.nxtbook.com/nxtbooks/newt...t_201003v3/#/0 where you can download the March 2010 edition and sign up for a digital subscription. Rather than using the web based reader program I suggest downloaded the PDF copy of the magazine to your computer so you can read it offline using your preferred PDF viewer.
Regarding the back issues on DVD, I'm interested but I want to know what format the magazine is stored in, e.g., PDF, JPG images of each page, etc. Sky & Telescope talk about having reader programs for both Macintosh and Windows but I want to be able to access the issues directly rather than being forced through a particular reader program. Currently nobody at Sky & Telescope is willing to say whether this will be practically possible. If direct access is made difficult by means of encryption or closed formats then I will not buy the DVDs.