Another major difference: Harvard is (if I'm correct?) incredibly expensive, whereas Oxford (at least for British students) costs the same to attend as any other British university and all fees are paid upfront by the government, with the loan repaid latet only under certain conditions. Obviously there is also further help for students from low income families, but I assume Harvard must have something like that too?
Jonah suggests that Harvard is no more expensive than American public universities. One of Larry Summer's projects was to increase financial aid and to make it more transparent. If he had remained president, I think it would now be significantly cheaper than its competition.
[Added: Solipsist made good comments that partially account for the phenomenon, and Douglas_Knight pointed out that the figure of $200m+ below should be $30m+]
This article reports that Harvard has 2,964 alumni worth $200+ million, with a total wealth of $622 billion. These figures are staggering:
Note that Bill Gates "only" has ~$75 billion and that Mark Zuckerberg "only" has ~$30 billion, so that they don't account for Harvard's decisive advantage over other universities.
What is going on here? Why would Harvard come out ahead by such a large margin? Its acceptance rate is smaller than those of Stanford, Yale and Princeton, but by no more than 25%. Moreover, this has been true historically
One can ask a similar question of University of Pennsylvania, which is significantly less selective than Yale and Princeton, but has a decisive advantage over them.
Some possible explanations for the discrepancy:
Regardless of which of these explanations hold, there remains a question of why they would hold.
Is Harvard a better choice than other universities for students who aspire to be wealthy than other top schools?