Nobody remembers Dunkirk because of deaths, jake. In fact it's scarcely a military memory at all; it's more socialist than that, to do with community spirit and determination.
I think jack's right, it's got a lot to do with the fact that it was within *living* memory. Commemoration of WW1 is now limited to November 11 and it's basically been broadened in scope to include the whole war, civlian deaths, dead soldiers anywhere anytime... Mafikeng and Azincourt are remembered, sort of, but no longer commemorated. As things slip out of memory, they'll slowly fall off the official calendar too.