Not wanting to digress here, but Terry Wogan is a poor example. His value to producers is his ability to ad lib. An excellent spontaneous entertainer.

He moderated a health conference I was a speaker at a couple of years ago. If there was ever a script, he must had memorised it beforehand. He certainly knew the agenda in his head. He introduced us all with no notes, including our backgrounds as if he knew us personally and was question master at the plenary session with no notes at all, including referring to things we had said during our own speeches.

Sometimes, there are reasons why the cream goes to the top.