Elephants are migratory over ranges exceeding 100 miles, so providing enough territory for them isn't really an option in a zoo setting.
This is true and I certainly don't disagree with you here. Perhaps my major gripe about a particular species for zoos is Polar Bears. afaik, the only facility in the world that is close to being capable of housing them is the Detroit zoo.
Every time I see Polar Bears in the typical enclosure you find--a self-contained glorified otter habitat with about 100 feet of walking space--I see nothing but miserable bears. It pisses me off, really.
In fact, I think Detroit takes in various number of Polar Bears from other zoos around the world because they have the reputation of being specialists.
I've only seen one or two zoos that have a good space for elephants:
NC Asheboro zoo--you rarely see these elephants b/c they are way the fuck out beyond viewing range in their simulated savannah space.