I don't know whether this was true in the 1940s, but today, sliced bread is extremely different from other bread. Not because of the slicing, but because it's a very different, longer lasting product that also happens to be sliced.
Not all sliced bread. The bakery at my grocery store offers all of their breads in sliced and non-sliced forms. I'm sure they put in some type of preservative, as it lasts longer than when I bake bread, but it lasts no where near as long as the sandwich bread that is sold in a different section of the store.
https://www.youtube.com/watch?v=i3sP2jwG9jc