Just a few thoughts.
Seems an odd marketing strategy to have two boxes with fairly similar size HDDs and not much price differential between them; just creates extra stock tracking hassle for retailers, I can't see them selling many of the 320GB box when the 500GB is only 20 quid more.
The Vestel SD HDD boxes I use at home also have the same quirk in terms of red button versus 'OK' having different options when recording, makes me wonder who wrote the SW for these boxes.
Will any of these Freeview HD HDD boxes ever be capable of copying recordings without hacking?