It has alot to do with our fiat currency. If we compared the price of gold at the time of penny candy, and figured out the percent of and ounce of gold that the candy cost, compared to the same candy per ounce of gold today we would have a close match on gold weight.
1950 gold = 34.72 oz
2011 gold = 1571.52 oz
( http://www.nma.org/pdf/gold/his_gold_prices.pdf )
so it takes 45.26 of modern valued pennies to buy what 1 1950's penny could buy.