I actually got a pretty good answer from someone elsewhere. I thought I'd share with you. I haven't checked the facts or anything, I took it at face value. lol.
"The standard proof for vodka has not changed in the US since the repeal of prohibition in 1933. Vodka is usually bottled at 80 proof, or 40% alcohol by volume (abv), so the answer in the case of Smirnoff vodka is, there is no difference in the strength. Spirits were, and are typically watered down to 80 proof to keep their prices down, since taxation in most of the world is determined by the level of alcohol in the bottle. Today more spirits of all kinds are available with higher alcohol contents than was the case in the 1950s, so in fact the answer with regards to spirits over-all would be that they are stronger today than in the 50s. Where whisk(e)y was also typically bottled at 40% abv in the 1950s, today the standard has risen to 43%, with many now bottled at 46% and a growing list of product available at what is considered cask strength, anywhere from 50-62% abv. American whiskeys bottled at 50% abv, or 100 proof, designated as Bottled in Bond (bib), have always been available, then and now, but they were far rarer in the 1950s than they are today."