Well spotted. The leads from RS come with 13A fuses fitted as standard. In the majority of our leads we remove it and fit a 3A fuse. I believe that the IEC sockets are designed to operate at a max of 10A continuous (15A intermittent max), so if the medical equipment draws more than 10Amps continuous, it can't use an IEC socket.
The in line fuses protect the equipment, but the fuse in the 3 pin 13A plug protects the integrity of the supply in the event of a short circuit.