I'd say the reason so many more people run Shimano over Campagnolo here in the U.S is simply because thats what their first bike came with. They start out on a low end hybrid or mountain bike which both a Shimano, then they decide they want a better road or mountain bike so they go back to the same bike shop and get a bike with Shimano. The After a while they decide they want some tools so they can do some of the work their self so they get Shimano specific tools. Then the want some new wheels and maybe a different cassette and the get Shimano Compatible. By the time they have invested all that money in Shimano they haven't got room for campy unless they have an ass load of money.