michigandermom,
Other than the self-selection I mentioned, another reason why it’s silly to use those percentages is that many research universities have larger percentage of majors not in liberal arts. At NU, 30% are in engineering and another 30% are in the schools of music, journalism, education, and communications, which include film and theater.
I was told by chemistry majors that there’s probably no better place to do chemistry at Northwestern. The number of chemistry students per year to number of faculty is roughly one to one! There’s no shortage of opportunities to do cutting-edge research with leading figures in the field (it’s ranked #4 in the world according to ARWU). The percentage of chemistry majors that go on to do graduate school is actually about 40% but the percentage relative to the entire student body is very small.