Frank,

I agree that if someone doesn't do the same job at the same level, then there should be a reason for pay differences. Figuring out "sameness" is tough anyway and it's why people that do the same job, say developer, have different pay rates. They're not much different, but because of seniority, experience, etc., they're different.

However, most women don't do anything. I've talked to HR people about this and while on average woman take off more time than man for leave, in any company, the majority of women do not take maternity leave during any tenure. That's because there are relatively few times when women have babies during their career.

As pointed out above, women often get paid less and it's simple discrimination. Or perception that they might get pregnant. It doesn't sense and it's not knee jerk to point it out.

Same performance, same job, same experience = same pay.