That's what I always assumed, until I started discussing rates with females that were hired at the same time, or before me, had equal/better qualifications, and definitely performed better than I did. I wasn't a great employee back then.
Also, I very much doubt you knew what everyone else was paid (I knew a few, but not most), so it'd sure be easy for you to assume that everyone was paid equally. That's pretty much the whole entire issue women are trying to raise. Men don't know and don't care so they just assume women are being "needy" or "whining."