When I did my A level selections about 6 years ago, I was at a boarding school with a mixed academic range (from very high to lower than people might "expect" from a fee paying school). This is when the norm across state schools was 4 AS levels then drop an AS and do 3 A levels + General Studies, thus ending up with 4. My school did not do general studies as an exam, so we would in theory have ended up with 3 A Levels.
We were told in no uncertain terms that there were certain universities who would look at our school and question the fact that we were only doing three when we were in a position to do four. There was no compulsion to do four (the school didn't push people who really would have struggled) but for those of us whose universities might have been leaning towards rankings like this, it was made very clear that four A levels would be expected and we would have to justify ourselves if we did not do them.
I think that's completely fair. I don't think it is fair to discriminate without asking. Yes, I had a good education and I don't doubt that some of my peers at university worked harder than me to achieve their grades, but that doesn't mean I did not work hard. I worked harder than friends at religious grammar schools who would, presumably, be ranked higher than me in this system.
I think the main problem is that there will never really be a way to give students from a less advantaged background an equal footing without also disadvantaging more advantaged students. I'm sure there should be, but I don't think it will really happen.