It is rare for Royal Mail to release imagery of forthcoming issues WAY in advance, as these days it often loves to keep its designs embargoed until just before the issue date. If ever there was a reason to always release designs early, this is it!
Perhaps the designers did this intentionally. Many of the photos of the Normandy landings include bodies in the surf. This photo could have been chosen out of consideration for the descendents, I.e. for reasons of "political correctness".
. Not showing dead bodies is more a matter of a decent respect for the opinion of mankind - especially the families - than of "political correctness".
Moreover, in a US stamp, it would honor the American wartime practice: the very first time an American newspaper was permitted to publish a photograph that included a dead American soldier was fairly late in the war. This was explained, credibly, as a matter of maintaining civilian morale (read "support for the war").
Lastly, there are zillions of D-Day photos that show the landings that are free of dead bodies.
One of them might even show my father, who was fond of saying that he crossed Omaha Beach "eight waves behind the nurses".