British, French, or German students may be getting a more rigorous liberal arts education in high school than most Americans do. So by the time they hit college, they are better prepared to specialize. I bet a typical Oxbridge STEM student knows his or her kings and queens, or 19th century British novels, at least as well as a typical Ivy League liberal arts major knows his or her Presidents and Herman Melville. As for deeper knowledge and skills associated with liberal education, I don’t know, maybe there is some advantage to prolonging general education past age 18.