Those older system came extremely late in the system's life cycle, when it was already phasing out. And the exclusive games for those were irrevelant. This one comes way too early and comes with a Xenoblade port right out of the gate (though even with new hardware, the preview video for that had abysmal framerate).
FWIW: the GBC basically took over and after a while all newly released GB games were GBC exclusive. DSi you'd be correct on.
As for Xenoblade: The original 3DS couldn't really handle it I don't think. The Wii is not exactly a powerhouse by any means, but the 3DS has a goddamned ARM11* running at 233 MHZ. Don't think it can handle the number crunching needed by a game like that without some major issues(Disgaea's DS port, anyone?).
*It actually has two, but I doubt the engine for Xenoblade is multi-core aware or would be able to get enough performance out of re-architecting it for a second core.