Easy when you think about it-The DS has a bigger install base.You can also play DS games on 3DS.I remember that after the PS3 launched someone asked Sony why didn't they put God of War 2 on that instead of PS2.They said the PS2 had a much bigger install base so it was better to try to sell the game to over 100 million than to the less than a million who had the PS3.That is exactly what Nintendo are doing now with Pokemon Black/White 2.
Does anyone know if Disgaea 1 and MGS:PW work on PS Vita? On my PS3 it says they do but they don't show up on my PS Vita at all.So could I download them to my PS3 then copy them to my Vita? Sorry for been off topic.