Questions about High Definition Video preservation

[UniSol GR77]

From the National Film Registry of Australia:

"Thankyou for your inquiry.
You will be happy to know that we do have the master Mad Max 35mm films preserved in the National Collection, we have also copies that are accessible to view here at the National Film and Sound Archive in Canberra, Sydney and Melbourne Australia. The masters have been copied to both Film and High Definition Video for preservation purposes and hopefully in the future we will also be able to preserve it in digital formats. We fulfil the worlds best practice in Moving image and Recorded Sound preservation practices with all the works in our collection so you can be sure that Mad Max is well looked after at the National Film and Sound Archive of Australia."

What is a high definition video?
In your view, is that enough to preserve movies the best way possible?
Why not on digital format yet?