The Americans appear to be more passionate about their koi and will spend much more than people in the UK or South Africa, using high tech filtration systems and expensive equipment. They will often only keep top quality Japanese Koi whereas South Africans will settle for normal pond fish and often low quality koi.
The quality of American koi seems to be better than in the UK and South Africa because they import most of their Koi. Obviously the quality of Japanese fish are by far the best.
The people in the UK are not very successful in breeding, probably because they have a very short growing season.
However, the Americans will also buy metallic koi and love the butterfly koi's. Butterfly koi are often referred to as "American koi". The Japanese do not like to breed butterfly koi as they see it as inferior to normal koi. The keen hobbyists in South Africa also do not keep butterfly koi.
The hobbyist in Japan will keep only Gosanke, although they breed other varieties for export. The average South African Koi keeper will buy the metallics, but the real keen koi hobbyist that enters their koi at koi shows will concentrate on Gosanke.