He's illustrating that the offset dropout will interfere with the caliper mounting plate, if the manufacturer were to try to move the caliper to the front of the blade without changing any of the rest of the fork design. But by having the dropout in line with the fork blade, and gaining the necessary offset by other means (offset crown and/or blades angled forward of the steering axis) the necessary clearance for the caliper mount could likely be attained on the front of the blade.