Inbreeding with chickens and turkeys is different than with peafowl. Chickens and turkeys are not kept for very long, so if inbreeding results in shorter lifespans, it's not noticed. In the wild, there are many mechanisms which work to reduce inbreeding. One is differential sex dispersal -- one sex remains, the other wanders off. Inbreeding in the wild is not a normal, regular, common occurrence. It happens when habitats are fragmented, populations are reduced, etc. I'll go into it more when I have time, but here's something to think about -- peafowl are not chickens. While they have some similarities with regards to care, they live long lives and are not consumed for food (generally). Chicken keepers are looking for maximum productivity with minimal input. This is understandable when raising a species for food, but since peafowl aren't raised for that purpose, perhaps they'd be better off from an aviculturist or zoologist perspective. With this, animals are bred for long-term captive populations in mind, not for cranking out as many as possible.
Ack, have to get to lab....be back later.