Pay differential is justified in a lot of sports.   The men's sports tend to be more popular and, as a result, advertisers pay more.   That's the way it is.

However, in the ordinary working world, there are all kinds of games played to avoid paying people for the job they do.   Most of the people who get caught by this in a significant way are women, in my experience.   Some of it is related to the way women approach negotiations and so on.   Some of it is sexism.  (See the article about the Tech world in the Globe yesterday.)