I found this strange as well, but after reading through the thread and thinking again, I may have figured it out.
However hard-coded "male" and "female" may have been when the game launched, the customization added later removed those limitations so it shouldn't be a problem, but then I realized the one exception.
Whatever "sex" a Sim is determines whether or not their top is covered, regardless of which "frame" they're using. I bet the reason this is limited to "male" Sims is because the scar would either be flat out covered by the non-removable bra/pixelation for "female" Sims, or otherwise is related to the built-in auto-censorship of "female" chests.
