I would like to ask you, politely, how it is you think they would port DS games? They have to cut half the screen and take out the touch support.
Also, the DS's main demographic is NOT children. It is made more universally, and it's main demographic is ACTUALLY males 16-23. Not really adults, but not children either, mind you. These people have access to the money to buy a psp. But just because you CAN spend the extra 200 american/300 canadian, it doesn't mean you have to. I could either A) Buy a PSP or B) Buy a DS and 3/4 games. I would choose the DS, if that were the only thing in question. Then there's the graffics question. A PSP can run PS2 games, basically (it's a little less, but w/e). A DS can run 64 games (again, a little more, but w/e). On screens of that size, the difference will be quite minute. Also, it is a portable, meaing that the average owner will not be enthralled with their system, since they are probably multi-tasking, with the game being only part of their attention. They will not stare into the screen and notice minute graffical genious. Really.
This is why people say the difference is neglagable. They aren't saying that the DS is just as powerfull, but when you think about it, the difference doesn't really matter.