As a reason the developer writes: "Do you know many issues happening in video game industry with regard to how to treat female in video game industry? We do not want to talk those things here. But certainly we have gone through in last year or two to come to our decision. Thank you."
There are many ways to look at this. Dead or Alive Xtreme 3 is certainly something that is questionable when it comes to taste, but at the same time this sort of self-imposed censorship isn't ideal either. Either way the game will see release in Japan at the end of February, and the way it's looking at the moment, you're going to have to import it if you're interested.