Because you need that for anything other than Nintendo 64 games--if you're using homebrew you can just use an emulator!
Neither the DS nor the Wii has excited me for a while. I love Brawl, Galaxy etc. though. I could stand to get Wario Land and some others if I weren't saving up, but most Wii games I've missed, I can get on the 360, where they're better... I need to start working... this summer and next year.
I'm always hesitant about the DS because my lite's shoulder buttons are dead and my old DS has a broken hinge and, being an old DS, has sooty screens that I hate looking at.
But I don't hate Nintendo like some fellows have come to. I don't have any Wii games that I can say have disappointed me--I've gotten what I've expected each time, and in the cases of some, more. Except the Zapper. I want more games that are made for the Zapper.