Adding iodine to table salt also added IQ points?

From Discover magazine comes this fascinating article on iodized salt in the US and how it may have added IQ points to the population:
Iodine deficiency today is the leading cause of preventable mental retardation in the world. It’s estimated that nearly one-third of the world’s population has a diet with too little iodine in it, and the problem isn’t limited to developing countries—perhaps one-fifth of those cases are in Europe (pdf), where iodized salt is still not the norm...