I think the DSi being released this late into the life of the DS is to get 3rd parties familiarized with making use of the cameras.
The 3DS will probably have the same cameras layout and might be slightly upgraded.
This way, the 3rd parties don't get thrown off by all the new features all at once. (Like how waggle took them more than 2 years or more to get good at)
When 3DS is out, they would not be overwhelmed with too many new things and ended up with minigames compliation of various features packed in 1 game instead of giving us the 1 full game.







