Saltfisher: There is no disputing the fact that a round tank, or a tank with rounded edges, is the better option in the long run for these, and other sharks. If it's feasible for a shark's tank not to have any flat walls, then that's the route I'd recommend.
That being said, I also think that some people take this "option" and over exaggerate it into an "absolute must." The problem is only seen when a shark is startled while in a closed container. If there are walls, he'll try to find a way past them. Round or flat, it doesn't matter. For the other 99.9% of the time, when the shark is cruising, he can see/sense the walls and will avoid contact.
Bottom line, an aquarium wall is just that ... an artificial barrier that the shark would not encounter in the wild, and whether curved or flat, will take some getting used to.