even tho its a wii, the usb wifi stick is a pretty standard device, only a small flash chip is programed with it's 'ID' different than the windows pc version of the same usb wifi stick.
the advantage of a usb wifi stick is that the usb cable can be long and have no effect on the RF signal, vs a pci/internal wifi which your stuck using coax antenna cable which will have an effect on the RF signal..
plus with their circuitry for the RF tx/rx splitter and amplifier being so close to the actual processor and rf driver you dont get as much noise compaired to again an internal/pci card which would need again more coax antenna cable, solder and tnc/sma connectors..
p.s. i dont own a wii so i dont know if the wii's usb wifi is really a pos or what. but i have used/tested a number of usb wifi stick's