As an aspect of truth in advertising nature photographers are now supposed to denote when publishing whether wildlife captured by camera are actually already captive. This is as it should be. Although the viewer doesn't always know from a photograph whether it was taken in a zoo or on the Serengeti it does a disservice to the profession for a photographer not to designate if the picture is of a managed animal.
For those of us who have traveled great distances at some expense and a lot of patience, heat, cold, frustration, etc. it matters. The thrill of the hunt is part of the appeal of wildlife photography and it's mind-blowing to get a really good shot after all that effort. Viewers of wildlife photography generally expect what they're seeing to be shot in the wild so it's only fair for them to be made aware when it isn't.
I've personally gone three places to photograph managed animals. You usually pay for a workshop that provides animals in natural settings. However, in one location I've paid a sitting fee for an hour and a half to photograph a couple of big cats. This is a great way to learn some of the "how to" parts of nature photography.
But it can't begin to approach the thrill of witnessing the everyday interactions of wild life where they live…whether it's your backyard or Botswana.