Polled bulls dangle their prepuce, the gene that weakens the muscle and leads to the dangling is linked to the polled gene. Makes the bull more susceptible to injuries such as sticks and burrs in the prepuce, or it being stepped on when the bull is lying down. Horned bulls dont have this problem.
In my similar question below, Knersie from South Africa posted a link to an interesting review I just finished reading. One of the conclusions of this report was it saw no advantages to horned vs polled except the tendency for some polled bulls to have reproductive organ problems. Production wise it saw no difference.
When I read "some..." it makes me think that 'some don't' By this I mean that if some don't the condition is not inevitably linked. What is being described is the status as it currently exists, an historical artifact, and not a predetemining limitation. If some do not have the reproductive problems then it can be bred out of future generations.