Two different systems, both of which seem to work well on their home turf.It can get confusing when users of one system encounter the other. On Denali, some years ago, we had to deal with some continental climbers who had experienced all the fun they could stand and asked for "rescue." We informed them that they weren't eligible and that they could just ski back down the hill. They seemed surprised that they couldn't just call for rescue when things got a little tough.

The North American system is based on volunteers, augmented by various agencies providing useful assets (helicopters). Capabilities evolve in response to different environments. (You would be surprised at the number of swift water rescues performed in the desert.)