One big problem with USB is that something might look like a storage device to the human eyes and hands, but it's actually a keyboard as far as the computer is concerned.
The U stands for Universal, and it's awfully convenient, but it contributes to the security nightmare.
A CD we can just passively read the bytes off, but if we want our keyboards to just work when we plug them in, then it's going to be harder to secure a supposedly dumb storage device.
