We just passed this law in Nevada last month. And you are right. When we first read the bill, many of us were quite vocal against the misdemeanor "domestic violence" prohibition, and also remarked that it was unnecessary, even if a good thing, because of the federal Lautenberg amendment.
I actually received a phone call from our most pro-freedom state assemblyman (well, technically from her husband) and he explained to me WHY they were doing it. It was complicated, but made sense overall. He then asked me not to spread around the reasons, because they didn't want the anti-gunners to get wind of the real plan, while they had their support because it was a line-item that added a prohibition.