If you ask me these claims are all valid but people don´t see the true reason why DS sales are slowing down in Japan: It´s the games. Brain Training, Mario Kart, New Super Mario Bros. and more have sold for more than one year straight in Japan but at some point those games have to stopp selling as well. If you compare hardware and software sales for the DS you´ll see that those games dropped together with the hardware after last years summer holidays in Japan.
In 2008 there haven´t been that many huge DS titles yet, which is the reason why the handheld sells less than last year. On the other hand the PSP is getting a bunch of new games, not only Monster Hunter and hardware sales show it.
If you ask me this is Nintendos fault to some extend. They released so many games while the plattform was still selling out in Japan that they don´t have any huge title left now. They should´ve saved at least some huge titles for this year but they are concentrating on the Wii currently.
We´ll have to see if Dragon Quest IX boosts sales for some weeks but currently it looks like PSP software sales are on the rise and the system is getting more big games in Japan while the DS is in a decline. That´s how the market works and if Nintendo doesn´t put some effort behind its DS developement in 2009 we could see the PSP outselling the DS for the rest of this generation in Japan. Because developers tend to look at current sales just as much as lifetime sales, which means they could shift some of their resources to the PSP.
Of course this doesn´t apply to the rest of the world where the DS will likely outsell the PSP by a huge margin for the rest of the generation. But Nintendo shouldn´t let third parties focus on the PSP, that´s not good, no matter how you look at it. (Of course it´s not that dramatic but hey, I thought Nintendo would be more agressive, that´s all. They seem to focus on the west currently.)
