Channel 4 and 5 specialise in this type of rather voyeuristic programmes. There's such a fine line between giving people a voice and basically turning them into a freak show, and I don't feel they get this line right.
However, there are plenty of people from the first world who appear in similar type programmes: people with dwarfism, Supersize/Superskinny. They never appear without the 'money shot' (so fat person naked, small person next to a tall person) just so we can all gasp.
The programme 'The Undateables' which I actually enjoyed had someone who had an extreme facial disfigurement due to neurofibromatosis. I know some people hated this programme, but I thought people were portrayed in a much more rounded and humane way, even though the voice-over was pretty patronising at times.
The most obvious answer to why there are more people from Asian/3rd world countries, this is what happens when poverty meets genetic conditions. In the NHS, this would have been treated. However, even with treatment, many people still live with disfiguring and stigmatized conditions, which it belittles us to stare at them, even through the medium of television.