First point: the assumption is wrong, SC3 is not a historical simulation. It is meant to be played as PbEM and has therefore to be balanced, which is already difficult, because the starting position is somewhat historical. It`s also a very differenciated game with far more depth than usually expected or even recognized; adding more lvls of differenciation doesn`t help balancing.
HoI is of course chosen intentionally, because it idealtypically showes how to ruin a game, if new lvls of complexity don`t work as intended (or perhaps do, to be able to sell the frustrated costumer updates and bugfixes as "features").
It does demonstrate why Germany and Japan put such a big emphasis on securing oil resources as soon as possible.
That`s not quite true, at least not in case of Germany. The only reason it came into play was the failure to reach the primary goals of their strategy, occupying Moscow or the destruction of the Red Army, otherwise their priorities would have been the Caucasus and the Middle East from the start. Germany had no significant oil shortages until Ploesti fell into russian hands. This also applies to manpower shortages, Germany was able to replace their workforce by slaves nearly until the last minute.
If those details had limited outcomes anyway, why should they be implemented? Would an A-Bomb have ended the war, even if Hitler would have been killed? Who knows...