It's worth noting that when someone buys an iphone or ipod touch, they may be buying a music player, a phone, an email device, etc. They're not necessarily going to be gaming on it.

When someone buys a Nintendo, they're buying a gaming device... hence the number of "apple devices used for gaming" (vs "apple devices capable of being used for gaming") is going to be way lower than the number of Nintendo's used for gaming.