ArizonaDocent, I agree that it seems like everyone I know has no interest in zoos and has not been to one in years! Zoo attendance figures must be partially composed of repeat visitors, or I just don't hang out with the half of the country that attends! To be fair, many of the people I know are in my own area and the local zoos are not generally well-regarded here by those who have not been (and certainly by some who have!).
Concerning Rio Grande, I wonder if their attendance figures include the aquarium and the botanic garden, which along with the zoo make up the Albuquerque BioPark? It does seem strange that their attendance was higher than Dallas, for instance.