You are right about those other birds actually requiring Iodine supplementation when in captivity, but I don't find it a good practice to assume that it is automatically applicable to all birds. See the study I linked in my previous comment for (scientific) information about Iodine toxicity in chickens. In my mind, if you care about a thing, you don't go haphazardly applying medications to it. In fact, if we did that to our kids, they'd be taken straight away.