Who cares if he said nigger, on or off air? There was no racist context, unlike his Mexican comments.
As a kid (not in the US), the only time I ever heard or said "nigger" was in that nursery rhyme, until reading Conrad and Twain. Just an archaic word like pickaninny.
It is kind of funny that some people now find it so taboo outside of any such context. Better not mention the Agatha Christie novel.
The joke (if you can call it that) is on the taboo word. You may have noticed that comedians like to swear?