The Wii is is built around innovative control methods. It's a relatively underpowered and cheap system that wins because it's so accessible. Nintendo have made a winner simply because they have opened up the world of gaming to a much larger demographic. You don't tend to have to many grannies playing Xbox360.
While I can't comment on a saddle controller there is no actual requirement to buy these things, just like there isn't for WM+, MK Wheels etc.