Axis & Allies: D-Day is, in many ways, a throwback to an earlier age in wargaming, when simulation definitely took a back seat to rip-roaring game action. Pieces fly off the board with such abandon that it's not unusual to see an endgame devoid of front liens as the surviving clumps of combatants maneuver like Napoleonic hosts around the objectives.
The entire A&A genre by designer Larry Harris represents, in many ways, a different way at looking at wargames from the mainstream hobby, although one that's becoming rather more common now.
Traditionally wargames have generally taken an organizationally-based view of warfighting, concentrating, except at the most tactical levels, on the organizations fighting the battle, rather than their weapons. Units are squads, platoons, companies, battalions, etc., all the way up to Army groups. This viewpoint goes right back to the origin of the hobby with Charles Roberts' Tactics, and the vast majority of wargames treat their pieces as military organizations.
The main exceptions to this have been low-level tactical games and games set in the ancient era, which more often break forces down on a functional or weapons-based basis. A piece will represent a certain number of tanks or spearmen, rather than an organization such as a company or cohort.
This isn't, of course, the only way to look at things, and it's certainly possible to consider battles as being fought by numbers of men and machines without over-emphasizing their organizational basis. Is it more illuminating to consider an attack as being by a tank company or by 17 tanks?
Harris' designs have taken the functional, weapon-based approach all the way to the grand strategic level, with the base Axis & Allies game. The Axis and Allies wage war with tanks, fighters and U-boats, not armies, air forces and fleets.
The latest iterations of the A&A line have moved down the organizational scale, but still reflect a functional approach to fighting. It's instructive to compare A&A: Battle of the Bulges with FAB; The Bulge, for example. Both games are at a similar scale, but one emphasizes the weaponry much more than the other.
In this light, it's appropriate to consider the Axis & Allies title an appropriate umbrella for the Hasbro line of military and naval miniatures, even though they're not designed by Harris and don't use his typical techniques.
Likewise, it's interesting to note that the functional approach has also found a new popularity among many of the newest designs. Borg's Commands & Colors system takes a very functional look at warfare in everything from ancients to World War II. Even Bowen Simmons' Bonaparte at Marengo and Napoleon's Triumph are largely functional in approach, although the latter title adds a little organizational touch with its corps commanders. But a corps in NT is defined by the number of infantry, cavalry and artillery blocks it has, not by its regiments, brigades or divisions.
Both organizational and functional approaches have validity. It's a matter of emphasis.