I had to watch motocross for quite some time to get into it and understand it. Well, I don't understand all of it...but I have the general principles.
I have come to the conclusion that American's like Nascar simply because the entire race can be viewed in one or two camera pans. No need to keep track of a certain racer-they are all in one camera view.
What part of motocross is most exciting? The first turn where all the bikes are in the same frame.
I don't think most Americans, including me, really like having to keep track of each individual car or bike. F1, motocross, supercross-etc. Now NASCAR? Sit back and drink a beer. All the cars are there and no need to think much.
That is a bit cynical on my part, but that is my conclusion. I can't think of many other striking differences.
I guess Europeans are far more sophisticated in that respect. But then again, are they not usually known for their sophistication?
There there is the fact one can park their winnebego right in the center of the track. Can't beat that American past time!