I am not convinced that it is explicit discrimination and, if anything, I think it is far more anti working class than anti women. If you perform well, you will continue to do well. The problem comes when people have bad patches (which, in banking, everyone does). That is when, if you are a member of the "gang", then you will be forgiven and allowed infinitely more chances (extended limits, extended time horizons etc etc). If you are not, it is very easy to freeze someone out.
In an industry where it is REALLY hard to objectively assess someone, it is very easy to subconsciously discriminate in favour of someone who is like you and, with a lot of senior management being men, it works in men's favour. In addition, the rituals one needs to go through to remain a member of the "gang" (presenteeism, always being contactable, being prepared to go out on late evenings etc) tend to mean that women get fed up before men.
Finance has many problems and, until a way is found to objectively see if someone is talented or not (and that is definitely NOT the case at the moment with the exception of a couple of areas such as pure quants, programmers etc), it will be hard to make it a "fair" employer.