I would think the majority of non-rich Harvard students don't pay much. For undergraduate studies if you want to attract the best students you have to offer very generous scholarships. Otherwise they would lose students to other top schools. This is true for all schools, but the rich schools like Harvard have the funding to actually do it. I've met a couple of students who paid full tuition at Harvard, but both came from very wealthy families so it wasn't an issue. Schools know in advance the financial situation of applicants and plan accordingly.