See if this helps - when I plug a 360 controller in, the game will automatically detect the controller. Having the ability to recognize a controller is not a problem in itself. But, if there were a "keyboard-only mode," the game would not recognize a 360 controller once it's plugged in. However, even in this "keyboard-only mode" there would still be a way to use the 360 controller, because I could use a mapping program (like JoyToKey) to convert 360 controller buttons to keyboard commands.
I know some people love the fact that games can automatically map an entire 360 layout, but for me, there's a major loss of choice involved. In my case, other USB-based controllers (like an N64 or Logitech) are actually more attractive for use with this game, because the game won't recognize them as controllers, and because it won't, it also won't force a controller layout.