Absolutely. And it isn't always about discrimination. People who consider themselves outsiders in the field will usually jump on the first offer they get, while the expected practice would be to get multiple offers and negotiate. They will also not ask for raises and promotions as much as their co-workers. Both of these result in a sizable disparity in salary, even though they may be higher performing than their co-workers.

Seeing a list of "here's what people around you are making" is VERY helpful to give one the confidence to finally ask for that raise they deserve.