Traditionalists believe that "true" sci-fi should have a real science component or deal explicitly with science and it's impact on people. See these definitions from Asimov and Heinlein:
Star Wars uses robots and spaceships to tell a fantasy story set in a space faring society, so by traditional definitions it's not really sci-fi. Its a space opera.
I'd argue modern Doctor Who isn't really, either. Its way more space fantasy than sci-fi. Old school Who depended on the writer.