Although either cassette (Campy, Shimano, or SRAM) can be used with either drivetrain, the freehub splines that fit Campy are different than the splines that fit the others. The splines that fit Campy are so robust that even when made from aluminum, the cassettes don't bite into them and mar them. The much less robust splines that fit Shimano and SRAM cassettes tend to be damaged by cassettes that fit them when the splines made from aluminum. It is only since 11-speed that the three brands can be used interchangeably with the different drivetrains. Before that you had to match Campy to Campy and Shimano/SRAM to either of those two. You still get to chose which type freehub to buy depending upon which type of cassette you plan to use.