As time goes on many of the actions for which the top tier medals were awarded will be partially-forgotten, only to be found in specialist books/web-sites.
Sure, Arnhem, BoB, D-Day, Dunkirk etc will go on being remembered, but a VC awarded early in WWII for an act that disabled a major enemy capital ship and incurred the loss of over one hundred of our own men still warrants more than a mere page in history. The medal being on display will bring that action to many, and thus increase their understanding of the whole of the war, not just the selected highlights.