It only took moments to learn how they dealt with the idea: it was avoided completely. Instead, you have a stupid AI opponent with infinite resources that constantly sends enemies at you in a single-file line reaching back to the barracks they're spawned from. This results in you needing to employ the same strategy every level: build up a any army to fend them off and at the same time build hundreds of pill boxes around your based until they can manage the endless hordes (which then become easy prey). So endless these waves are, I once left the computer running (and increased the game speed) as I left for the day, later to beat the mission in progress. In the end, the AI opponent sent over a hundred thousand Prussians to die pointlessly. Realistic? Well, in a way yes, but if it were... uh, a better designed game that tried to play off the source material, certainly there would have been a 7 day long artillery strike and then waves of soldiers being thrown at me (and at least some would be able to break through).
But what could you expect from a game that runs off of a somewhat antiquated engine? If you want trench warfare, craters as cover, etc. we might have to wait a few more years before anyone will try to tackle making this conflict into a game again. But will it be good? So far, not a single game has done it right (though some were fun).