Who Gets To Present Papers

I'm starting to realize how many small things are different at not only different places but different fields in academia. One of the hostel mates is studying nano technology in Spain. When he publishes a paper, especially if it is an important conference, he doesn't get to present his work. Instead, his advisor gives the talk. Not only that, the student doesn't even get to go to the conference if it is expensive and far away. He's limited to travel only for poster presentations at small workshops located in the vicinity around Spain. Anything more substantial and only the professor goes. Maybe computer science is one of the few fields that expect students to give talks at conferences instead of professors...