Why are Oxbridge offers so low?Watch
My Cambridge offer is a clear five points (I do IB) higher than any other top university gives.
Essentially, the primary reason this is the case with arts subjects is because the difference between an A and A* in something like English Lit or History is significantly more subjective than with science/maths subjects, and not necessarily an indicator of someone who is better or with more potential.
You also have to remember that Oxford does research the statistical significance of certain factors in determining success at the undergraduate level. The entry requirements remaining at AAA would logically seem to indicate that there isn't a statistically significant difference in the success of undergraduates in these subjects on the basis of A/A* at A-Level.
As to why Oxford would keep them at AAA when competition is 7 applicants per place, and universities with less competition have higher requirements - simply put, Oxford has more information on each applicant from admissions tests and/or interviews and so can afford to discriminate based on other factors that they may, or may not, have found to be (statistically) significantly better predictors.
Relatively speaking of course, most Oxbridge offers are A*AA or lower, no different to any other top 10 unis- why is this? Academically speaking they're no harder to get into than any other elite Uni, it's just interviews that separate them
If someone were applying for English at Oxford for example, and they were studying English, Maths and History at A-Level, it may seem a bit excessive to give them an offer of A*A*A*. If they rejected them for getting less than an A* in Maths, they could well be losing out on a candidate who is an absolute prodigy when it comes to English. It's not as though the lack of A* in Maths is going to make them a worse English student, because they're totally different subjects.