Actually, the PS2 does use normal USB. But to save space they used a propietary driver-ish. It's still USB, but it needs a playstaion certified controller. That's putting it simple, it takes a bit to explain. Basically, you know when you first plug a USB devise into your PC, it is detected and the computer "knows" what the hardware (like Logitech Gamepad). That label comes fromt he USB device.
Anyway, guess what, you can plug any logitech wheel and it will most likely work in the ps2. Hehe, you may know the official ps2 wheel is a logitech too.