Wow. If that's true, I can't believe Twohy would be adamant about that. It wasn't like you got a full on topless shot, it was mostly a side shot of one breast. And that was unnecessary to include. Don't get me wrong, it was a welcome shot, but still, it wasn't needed at all.
And if Twohy was so insistent, they could've used a body double. And they already had shown some topless female Necromongers, so he had the boob shots he maybe felt he needed to be edgy and/or get the R-rating.
When I think back about it, while Katee did a good job and on one level was tough and competent, she was highly more sexualized than Radha Mitchell in Pitch Black and Thandie Newton in Chronicles. It was like a step back, maybe an attempt to appeal to the proposed juvenile (in thinking if not necessary in age) male audience or fanboys. I also think that there was a regression in how women were treated and depicted in Riddick compared to the other films. Even Katee's name, Dahl (pronounced doll) stuck out to me. I don't know what they were trying to suggest by naming her that.
Keri Hilson's brief cameo, where it was suggested she had been raped by Santana's crew and then her character was offed without even given a name. In comparison, the female characters in the other films were written and depicted much better than what we got in Riddick.