Notice however that virtually all of the decline takes place on the inward journey, when it was still summer. The reality is most of the losses came from desertion caused by inability to supply so large a force. He could not move rations from his stockpiles to the army efficiently, because it was advancing rapidly and his supply of horses was quite limited. They died first. Men trying to live off the land found it practically uninhabited compared to what they were used to in western Europe, and strayed far from the main body looking for food. Often as not, they found cossacks instead.
I too have pondered that graph on more than one occasion and had the same observation/question. Napoleon launched the campaign with some 600,000 men, roughly two thirds of them in the main body and the remainder in detached forces guarding his flanks. By the time of Borodino, the main body was reduced to about 120,000. About 100,000 reached Moscow, and somewhat fewer started out on the retreat. I'm writing from distant memory so give me a little Kentucky windage here, but that's in the ballpark.
While the retreat was a catastrophe, the fact remains that most of the army had been attrited during the advance. I wonder if someone here can point me to a more detailed analysis of the losses. Presumably a much larger percentage of the flanking armies survived the campaign than was the case in the central army group. One would also need to adjust for troops detached for line of communications duty and sick men left in hospitals and eventually invalided home (or back to Germany) during the summer. Plus desertion.
None of this alters the fact that the campaign was an unmitigated disaster, but "they all froze in the snow" is neither accurate nor satisfying. Does anyone have a good handle on this? I plowed through David Chandler's big book on Bonoparte years ago but am not otherwise familiar with the literature.