I think the other issue is the new iPad, new iPhone, and iPad mini retina are apparently all launching this fall season. That's going to be on the top of a lot of kids' wishlists for Christmas gifts. 3DS simply has it much tougher than the DS did.
Lots of kids are getting these items (or simply using their parents) instead of the traditional gaming handheld from a young age.
It's pretty much entirely why the 3DS probably will never be able to top 20 million shipments in a year, whereas both the GBA and DS did that, the DS even crushed 30 mill for a couple of years (amazing).
Tablet/phone market has definitely shrunk the 3DS market and basically killed Sony's handheld market entirely. In a way I think Nintendo has to push harder each year to prevent year over year declines against the eroding effect of smart devices. To sell 15 million 3DS' today, they have to work much harder than it was to sell 15-20 million DS' 4 years ago.
