I have never understood that. I could see if maybe the controller port on the 360 itself was that big circle connector, but it's not. It too has USB ports for the controller hook ups. So is there any reason that you can remove that adapter?
This isn't so much a rant as just a general musing. Because I recently got Steam and found it to be compatible with 360 controllers...the only problem is, as you guessed it I'm missing that little adapter that will allow me to plug it into a USB port.