NASCAR

I don't consider myself a diehard fan of NASCAR racing but I do enjoy watching the races. This is what I don't understand. What's the difference between the NASCAR Craftsman, Busch, and Nextel series? If I'm not mistaken many of the drivers race in two or more different series each week. And why isn't auto racing an Olympic sport? There is a lot more action than sailing. Wake me up when they raise the spinnaker.