I believe iodized salt was the only option here years ago. As tastes have refined and people become more educated, Kosher salt is the prefered salt. I would imagine that cheap restaurants and fast food places would use iodized salt since it's cheap. I would think that any restaurant that has a chef as opposed to a short order cook would use Kosher.
Sea Salt is quite a fad here now as well. People here are super aware of food now and any decent restaurant, even a chain like Chevy's or Applebee's would be able to tell you what kind of salt (or any other ingredient issue you might have) is used. If iodine is an issue, I would just look for low sodium options. Certainly people watch their salt intake not just for the iodine but for other health considerations.
I'm learning more and more about cooking for myself and I find I enjoy the food I make when I KNOW the ingredients are fresh and what I put into my meal. Even when traveling, it's better to find a salad bar and choose what you put into your body.