This sort of relates to this thread & Tipsy's other thread about how many A levels are taken at different schools.
Cambridge has made some offers this year based on 4 A levels - obviously it cant do this where students are only taking 3 A levels! but it rather begs the question as to whether 4 A levels is going to become a requirement of Cambridge over the next few years? Or will it provide different offers for those coming from the high performing schools where 4 A levels is the expectation against those coming from more average Comps?
Your second idea sounds fairer, but I would be uncomfortable with the idea that a very bright student who could get 4 good grades does not have to try as hard simply because they attend a school with lower expectations. This would also unfairly discriminate against those at higher achieving schools.
I know of one comprehensive which states quite openly in its prospectus that most sixth form students do 3 A-levels in Y13, as this is all that is needed by universities and employers...
. It also takes students to open days at Cambridge, so presumably the university is indeed prepared to make allowances since most of the visitors will only be studying 3 A-levels?