I'm not really twisting things though, am I?
The second world war and the associated rapid progress in technology, design and industrial processes changed the world far more in a shorter period of time than at any point previously in history.. and a lot of the research that was carried out during the war obviously made its way into the public realm afterwards as can be witnessed by the more streamlined styling of cars, planes etc.
The RAF started the war flying biplanes, yet by the end of it had jet fighters.. That's the level of advance we're talking about (let alone we suddenly found ourselves in the atomic age) and something that was applied across the board, be it transport, weaponary, medicine, electronics.. Even looking at weaponary, yes the Tommy gun was used during WW2, but we also saw the precursors for the likes of the AK47 (Stg44 for example) and other more advanced weapons..
So my assertion that there's a gulf of difference between the late 20s/early 30s and late 40s (LA Noire is set in 1947 mind) isn't far off the mark...