Getting a bit off topic, and not really answering your question...
One thing you should keep in mind, Bartman, is that zoos don't really save species, with a few notable exceptions. Their main role in conservation is public education. Since habitat destruction is often the major cause of a species' decline, breeding a few in zoos doesn't really rectify the situation. Often, the number that have to be taken out of the wild to establish a captive breeding population does more damage than good. As I said, though, there have been notable exceptions.
As far as zoos go, most investors that might be interested in funding your zoo will want some return on their investment (unless they are doing it to raise the profile of their company by being seen doing a 'good thing'). That means the zoo has to make a profit. For zoos to be profitable, they often have to get the big ticket species, which are often non-endangered, but (to the public, anyway) spectacular animals. Most of the really endangered species are little obscure things that make poor zoo exhibits, their obscurity being part of the reason there aren't already huge campaigns to save them. A classic non-conservation oriented, big ticket display is the white tiger. It's a captive propogated genetic freak, not an endangered wild animal that needs protecting, but brings the punters in. Therefore a lot of zoos use up a fair bit of exhibit space and food money housing white tigers because it will help pay for all of the other, boring (to the public) species.