I dunno if I'm free to discuss this, but I have to point out that Diablo has a sexy walk in one of the later cutscenes. It's when you see him walk away and you're looking at his behind and you see those child-bearing hips. Diablo is freaking sexy, guys.
I think you're assigning the wrong gender to Diablo...I know Cain calls the three prime evils brothers, and claims Andariel was the only female, but Diablo's always had these feelings of being born in the wrong body...