I hear what your saying, but admissions personnel, will always spout what is in their prospectus or literature. It's their job to do that, and to not put off people applying. Yes GCSE's may not be there main criteria, but that is the same with Oxbridge, who also Spout the minimum number of GCSE grades to get in, being a B in Maths, English etc. But it's no coincidence, that all their offer holders and people who eventually get in, have mad grades at GCSE, usually 10+ A*s and the like. These top universities, will think if you slightly struggled at GCSE (Although 4 A*s at GCSE, to me, is not struggling), they will look at whether you would be able to cope on their respective demanding A100 Medicine courses. Top Universities are always over subscribed with applications from high achievers, so they have the pick of the bunch. It's therefore, not surprising, that most of their cohort intake have near perfect GCSE's.
So having a good set of GCSE's is a good start. Not having strong GCSE's, is also an easy way to eliminate you, if they have to decide between you and another candidate to invite for interview.