You're forgetting that the 3DS CPU is most likely consisting of two separate ARM units of equal processing power. One can be underclocked to the DS/DSi level to play the game, the other can deal with the menu in the meantime.
I assure you, the 3DS isn't capable of "emulating" the DS - it hasn't got nearly enough processing power. It can only mimic it at best.
The Wii couldn't perform such a feat simply because it could not Multitask. The 3DS is designed for multitasking.
I assure you, the 3DS isn't capable of "emulating" the DS - it hasn't got nearly enough processing power. It can only mimic it at best.
The Wii couldn't perform such a feat simply because it could not Multitask. The 3DS is designed for multitasking.