One of the things even the high-powered public speaking trainers tell you is that the only way not to be nervous is if you no longer care. Any time you have an audience you actually want to learn something or be convinced to take some action, you should feel a bit nervous.
To my surprise, Ed Witten, one of the preeminent physicists of our time, is quite gifted in public talks and interviews from what I've seen of him. You'd expect someone explaining string theory to laymen to throw in a few "ums," but they're quite rare in this and other interviews (https://www.youtube.com/watch?v=f1BcyxQCnoE&feature=rela...). I find it inspiring, as someone who's had issues with public speaking in the past, to see such a brilliant man handle a conversation with such ease.
All sorts of people can get nervous speaking in public, including people that are thought of as being 'natural' public speakers like Steve Jobs (http://www.youtube.com/watch?v=FzDBiUemCSY) and Sam Harris (http://www.samharris.org/blog/item/the-silent-crowd-overcomi...), as well as billionaires (http://www.quora.com/Peter-Thiel/How-is-Peter-Thiel-so-amazi...) and CEOs (http://www.youtube.com/watch?v=o3hu3iG8B2g).