I’m comfortable doing it, and generally receive positive responses, but I’m not “a natural.”

If I have something that I need to “get just right,” like a class or main speaker gig, I have to practice a lot, and can come across as a bit “stiff.” If I don’t practice, I do well, but not predictably so, which makes me a bit of a “wildcard.”

I know quite a few folks that can walk up to a podium, in front of hundreds of people, at little notice, and knock it out of the park. They often practice.

Steve Jobs was one of the best public speakers I ever heard, and I’m told that he used to practice for hours. I knew a woman (I’m friends with her ex) that used to regularly appear on TV, and keynote finance conferences. She has an “aw shucks,” casual style. Her (ex) husband told me that she’d practice before each gig for many hours.

The folks that make it seem to be “natural,” at anything, generally practice a lot. I speak frequently, but it’s not structured practice.

I suppose it's a combination, some people are more comfortable speaking and improvising on the spot but everyone needs to practice. I can add to your list a CEO of a big bank, he speaks freely and it's a pleasent to listen to him, but I heard that he practice using a private instructor as well