I don’t know if I buy that that arbitrage is so possible. If you buy a textbook cheaper in Thailand, and sell it for more in the U.S., you are adding a lot to the cost in transporting it. Sure, this girl did it as a one-off, but is there evidence this is cost effective for some large scale enterprise?
All I know is that the U.S. publishing industry thought it was a possibility, and spent a lot of money (way more than the amount of damages claimed in this case) to bring the issue all the way to the Supreme Court.