I would have thought that is more down to the nature of the game itself.
I own a PSP and a DS and the psp hasn't left the house in four years (it doesn't get played at all anymore to be honest) because the games just aren't conducive to a quick play on the move. The DS has loads of quick 'pick up and play' games as well as some quality more in-depth titles although, as you mention, much of the lighter content has lost it's appeal due to smartphone developments.
Playing anything more than a point and click variant on a touch screen is a horrible experience though.
Similarly, I recently met with a Japanese development team from Nissan and they all have iPads provided as their work computers but I honestly can't think of anything worse than typing out long entries using a touchscreen keyboard.
