There were at least two other actresses in the movie who were nude, and one of them was Jaime King, who already established a name for herself in the Hollywood when she was in the first Sin City. To me, it seems like Alba was pulling a diva and made an excuse that her military dad won't approve of her so she couldn't do nude scenes, but in fact she probably felt like it was beneath her status to be naked on the screen. If she felt so strongly about it, why did she accept a stripper role in a R-rated movie based on a graphic novel where her character was nude in it?