A passing comment by Axis & Allies designer Larry Harris on some forum helped put his classic Axis & Allies design into a different perspective for me. He remarked that in order to be historically accurate the U.S. should have double or even triple the resource points the game gives. The lower number is used for game balance purposes.
Given this design note, I think it's fairer to consider the standard Axis & Allies (and all its related strategic level games like the Revised, Europe, Pacific and upcoming Anniversary editions) as really being an "alternate history" of World War II rather than a model of the actual conflict.
This isn't as unreasonable a design approach as it may seem, either. While the common perception today is that an Allied victory in World War II was inevitable, if wasn't seen that way at the time -- especially from the perspective of 1941 or 1942 when the game starts.
Richard Overy's excellent book, "Why the Allies Won," explains how an Allied victory was far from inevitable. He outlines a number of critical factors that played a huge role in the outcome of the war, but one in particular is notable in the context of Axis & Allies.
One advantage a simple game like A&A has over more complex treatments of the same topic is a certain freedom from constraints. Usually a more detailed design adds more and more restrictions on what the player can do. While certainly justified from one perspective, as the real world is indeed full of constraints, it also means that the game player is forced to accept the designer's premises. The necessity of keeping a complex design manageable will keep the designer from straying too far from his design parameters. A complex simulation of World War II will have to stick to the historical script on the really macro issues such as economic mobilization.
But the differential between the economic efforts of the Axis and the Allies was one of the key reasons for the outcome of the war, according to Overy. In particular, the Americans and the Soviets each, albeit in different ways, mobilized their economies far in excess of what the Germans thought possible. Meanwhile the Gemrans, despite having the resources of all of Europe and an educated, skilled workforce, didn't make the most of what they had. Those interested in the details of the argument are directed to Overy's book, but the bottom line is that the Soviets were able to outstrip the Germans despite having an economic base just a fraction of the size. And the Americans were able to switch over from a peacetime economy to a fully mobilized war effort in a little over a year.
So, while it's true that the Germans were overwhelmed by superior numbers, it's largely their own fault. Had they mobilized an effort comparable to the Americans than the war might have turned out quite differently. Indeed, once Speer took charge of the economy the Germans started to turn things around. But just as Speer's reforms were beginning to bite the Allied bomber offensive started to hinder the German economy effectively. It was a near-run thing. Had Speer been put in charge six months or a year earlier, the bomber offensive might never have been able to really get going. (That bomber offensive is another of Overy's key factors.)
Axis & Allies allows some experimentation with the potential consequences of a better German economic mobilization by increasing the number of German resource points.