I think the change has been in volume. In the US at least much of the food you take off the shelves (especially of the "microwave dinner" variety) have large amounts of sodium. I know this is an extreme example, but take a look at the sodium content in those popular "ramen noodle bowls" (styrofoam cup, not in a bag). That's more than 100% of your RDA of sodium right there. They do not taste overly salty IMHO.