McG is right on target with his answer.
FYI - The reason a cyclocross bike closely resembles a road bike, is because cyclocross grew out of road racing. In the old days, roadies would put knobbie tires on the road bikes to train in parks, fields and woods during the winter time. Because the speeds were much lower than riding on the road, they could continue training during cold weather. Being competitive sorts, training rides soon became races and the sport of cyclocross was developed.
As the sport developed, cyclocross bikes became more specialized for off-road riding. Thus, the bikes have cantilever brakes, wide tire clearances, interceptor or interrupter brake levers, etc. Still, they look and function quite like a traditional road bike and, in fact, with regular road tires, I ride mine on the road when my road bike is out-of-service or I want a change of pace.
Hope this helps.