Not true, at all. There are plenty of split crown races used in modern headsets, and, most of them can be easily pressed on by hand. They are, of course, exclusively used with cartridge bearings that supply their own bearing races. With non-cartridge type headsets the crown race supplies one of the two races needed for the bearings. All a split crown race does is provide proper spacing between the fork crown and the lower bearing cup (which, again, is not supplying a bearing race in a cartridge type headset).