Its reached the saturation point. Maybe its time for Nintendo to release a new DS design in Japan or cut its price.

I blame these two for the popularity of PSP Slim in Japan.

New design and new color, and saturation in Japan for DS.

Everyone in Japan already has a DS and PS2.
No one in Japan cares for Xbox360.
The Wii is supply constraint (i think)
And the PS3 is too expensive (especially considering the economy), and does not yet have the library that the Japanese audience wants.

So that really only leaves the slim massively multi colored PSP.

Everyone in Japan probably already owns the DS so they are now buying a PSP.

Japan is a much-more handheld-oriented region than the US and EU . The DS reached its saturation point , so its obvious that the next system they will move onto will be another , different handheld .

kingdom hearts birth by sleep says hi

You and me,soriku know that’ s the real reason why japanesse gamers are buying the psp.

Well both PS2 Kingdom Hearts games outsold the PS2 Monster Hunter games significantly.  Whether it will have as much handheld popularity as MH is yet to be seen.

KH games outsold Monster Hunter games in Japan alone . Still , MHF games are much more popular than anything on the PSP , so I doubt it that KH : BBS could be it ...

I meant in Japan only.  But hunter already mentioned that.  The best selling MH (PS2) game 600k.  The best selling KH game 1.24 mil.