You're assuming they're equally talented, you don't actually know that to be the case. Even if that assumption is correct, talent isn't the only factor that determines salary. I don't think employers actually have the data they need to ensure the wages they pay closely correlate with productivity. If Google isn't intentionally paying women less because they are women, then I think the answers to these questions pretty much has to be 1. Because they can & to save money 2. Because they can't 3. Because they're operating under the same set of assumptions as everyone else in the industry, and better heuristics would probably cost more than they'd save on labor.