I found this disclaimer on a packet of sea salt: "This salt does not supply Iodide, a necessary nutrient". Two questions arise from this:
Does salt naturally contain iodide? No
Do most people in Hong Kong need extra iodide? No
Iodide is added to most salt that you buy, and has been for a very long time. The warning on the salt I bought is apparently mandatory in the United States. However, for most people with a reasonable diet, there is no need for extra iodine because it occurs naturally in fish, some vegetables and some meat. The bad news is that insufficient iodide consumption by mothers and children is the leading preventable cause of mental retardation (more here).
For people with very poor diets, the iodide added to salt can make a big difference. I read an article some time ago about one very poor part of the world where non-iodized salt was being sold much more cheaply than iodized salt, and this had led to a marked increase in mental retardation in the local population. Unfortunately I can't find the article or remember any more details about it.
The irony here, of course, that people who buy sea salt in a supermarket in the United States (or Hong Kong, or other rich countries) are the ones who get the warning, and are the least likely to need to worry about it.