Adding milk to very hot tea can result in the milk being scalded, giving a taste rather like that you get when using UHT milk - a taste many people dislike. Milk first, then tea, and this won't happen.
Speaking of teabags and luke-warm water, I'm utterly convinced that Lipton's Yellow Label teabags, invariably offered worldwide, are specially blended to provide a drink with a tea-like taste when used with luke-warm water...(also invariably offered worldwide).