How distinct was 1940s US culture from the 1930s? To me, a European born much later, the 1940s are the decade of 20th-century American aesthetics that blends the most into the previous. The changes I see are all related to WWII. Civilian everyday life captured in film and press photos seems the same as in the 1930s.
I think the 1940s war time culture is pretty distinct. Aside from that, I agree, those are probably aesthetically the most similar of the bunch.