That may be true, but I don't think it's overt sexism, if anything I think it's likely to be a cultural problem similar to the differences in college major. For example, one of the variables that the 77 cents on the dollar figure failed to control for is that men are overwhelmingly more likely to negotiate themselves a better salary, while women are more likely to simply accept the first offer without negotiation. It would not surprise me in the slightest if the same personality traits (which can be heavily influenced by cultural norms) that make men more likely to negotiate salaries also makes them more likely to aggressively put themselves forward for promotion. Which is a legitimate gender issue. But one that is cultural, which means it's wrong to then jump straight to "corporations are sexist".