Ds is bumped up N64 technology not gba's.
I have a friend who does homebrew for DS.
You have the GBA API in there in its entiretiy. Same processor for one screen, a newer processor for the other screen. There are new modes and new functions for the new DS bits and you address each screen separately.
NDS does NOT have a Silicon Graphics in it.
EDIT: My point is: the fun you have with a console is related to the software in it, not the hardware that it runs. DS is *also* a small upgrade to existing hardware. Only devs have used it much more wisely than Wii's (still waiting for proper DS RTS tho)
What really hurts Wii's graphics is that it doesn't have shaders but a customisable(?) fixed function pipeline. Imagine you only had Construct's effects to do everything. You can mix and match but you can't write specific new effects.
Developers today are *really* used to shaders (and yeah they're sweet), thus they barely use effects on Wii. I'm sure we'll see a new version down the road with proper graphics and mature controls (including sticks, buttons, cross, motion and pointer)