In an interview, the Sony producer of DS said that the continuation of the DS's IP was dependent of its sales in the US, not Japan. At that the time the game had already been released in Japan a long time ago and it was coming to the US. So the decision of not making a DS2 (if real) has nothing to do with Japanese sales. The game sold, and keeps selling, more than initially expected. The only reason why they would not make DS2 would be if Sony was diverting resources to something they consider more important and not because of DS sales beying bad in Japan (or the US for that matter). Fuck, they even said they should have released the game themselves in the US and letting Atlus US release it was a mistake.