If you look at the type of photography that he did and the conditions that he took them under, there was no way that he could carefully meter every exposure. War photos, quick shots that he had to fire off, really low light situations, etc. He was a photojournalist and he just couldn't take the time to meter accurately for every shot. Also, he shot roll film and had to develop each negative the same amount of time so he couldn't control development for each individual shot. In fact, he would roll 2 rolls of film at once onto a reel and develop more film at once that way. He wasn't interested in producing a technically perfect negative and, given the way that he worked, he couldn't do it even if he wanted to. He was able to pull great prints from these negatives, however, and that is what really matters. I'd say his real craftmanship was in the darkroom. EWS also had personal issues with alchoholism and he might have had a mental disorder given his constant emotional agitation. He was self-desctuctive. This just doesn't sound like someone who would stand behind a view camera carefully calculating exposure and development times before taking a picture. Sticking his head up from behind a rock to capture an image of some marines setting off an explosive nearby sound more like his style.
I have seen a fair number of his original prints and they are beauitful, so whatever his technical approach to exposing\developing negatives was, it worked for him and that's all that matters.