Because they only put on the minimum possible grades that they will accept , but to get in on the low GCSE grades , ud have to show a serious turn around in ur AS results and have an amazing personal statement and work experience ,
thing is theirs a lot of applicants who have the A2 grades they want so they have to find some way of seperating them , and the likeleness is the ones who did well at GCSE are the ones who are really commited to medicine ( not saying that people who didnt do well at GCSE arent commited to medicine )
End of the day is they need to kick out about 10- 15 applicants for every one they take , and if 2 people match at every other point , they take the ones who did better at GCSE
I only have 3 A* but im working seriously on my interview technique and personal statement cos even with few A* i still got 2 interviews this year