As a youngster I was terrified of public speaking, and could barely get words out. Now I have to give talks as part of my job from time to time (gave two last week, in fact), and I love it. I can't say exactly what changed besides my age, but I don't get nervous now at all. Its at least partly from practice, and partly from the realization that no one cares (or likely will even notice) if you make a mistake. I think what makes many people uncomfortable is that we live in a culture where modesty is valued, and it just doesn't fit most people's personality to command everyone's attention.