I should clarify that statement. What I was meaning was simply that I don't think more boots from WWI would exist than WWII boots if they were simply made from regular horsehide. I've never heard that regular horsehide is more durable than cowhide. If it were, I think it would be far more prevalent today.
I agree that EG isn't in it for durability. The more shoes they sell, the better off they are. However, the article is pretty clear that shell cordovan was a "normal" material for shoes and boots in Europe back then, before resources started drying up in the 1930's (most cordovan was produced in Germany). I think the article is definitely saying that cordovan was the preferred material for army boots at the time, for it's durability. Don't forget that horse meat and horses in general were far more prevalent back then when horses were the primary mode of transportation and were used for all kinds of work. It was a different time. Just about everyone owned a horse or two (or more). They were "necessary" for daily life.
Makes enough sense to me. However, I'm not sure I agree with your historical analysis of the horse. By the 1920s more people were living in urban/industrial centers than in rural areas, at least that was the case in the US, Britain, Germany, Japan, and other developing/industrializing nations. In any case though, it is likely that horses were more prevalent back then, than now.