Yes, you would need the official XBox wireless adapter.
Just like even though I had a PS2 USB adapter, I couldn't use my PS2 controller. Also couldn't use a Sidewinder (who makes those again?). And the XBox Live Vision Camera is the only camera you can take pictures with. Not just any ol' webcam.
And to use the 360 controller on your PC or Mac, you'd need a special driver. There's something different about this USB. It doesn't quite give us the freedom I was hoping for. Gotta wonder... My keyboard works, but if a game should have mouse support some day (please God) will I need an XBox mouse?