I think that given the right owner and care, captive peafowl can live longer lives than their wild relatives. In the wild peafowl might be weary but they will not always escape danger as they do have predators, like one of the mightiest predators of them all, the tiger.
Here is a video showing a tiger stalking and killing a peacock.
http://www.arkive.org/indian-peafowl/pavo-cristatus/video-16d.html#text=Threats
In captivity peafowl are more protected from predators and because they have us to watch them they can be treated if they become sick.
Sure peafowl might be getting all the nutrition they need in the wild but that doesn't mean they are living longer lives exactly because other factors come into play. Wild animals will always be more beautiful looking than captive ones that is just how it goes. You can work hard to feed a captive peafowl a diet that you "think" they might be getting in the wild but unless you have it in a huge self sustaining aviary in India you may never get the same exact effects.
Most peafowl breeders care about their birds, but like Deerman has said we all have our own way of feeding and caring for our birds. It all depends on what kind of feed you have available and how much you can spend on feed, etc.
Anyways this is a topic about the feeding of peafowl from Deerman's great experiance and I don't think we really need to get in a whole debate about wild peafowl and how long they live and all this other stuff that will just get off topic when really this is deerman's topic to help give information to new peafowl owners or peafowl owners who want to feed a new way, etc.