After my wife's parental leave had ended, I tried to persuade her to ask for higher salary than she had originally intended. Sometimes our discussions even turned into arguments and, in the end, she asked for what she felt was adequate.
Now, from my POI it feels like I was forcing her into a place she was not comfortable to go to, or she was even scared of.
This will probably be labeled sexist but, I wonder if some natural lack of boldness, daring or arrogance does not play a role in what we perceive as a artificial gap.
Also, as a visual designer, I've looked at that chart and two things came to mind: “Dang, I really must suck as a designer if I can't get paid more.” and “Yeah, why not. If women can recognize more colors, why couldn't they be better visual designers and get more money for it?”
But I can just be an eastern-european sexist ;)