Well first of all, importing prescription drugs is a bad analogy - completely separate issue. It's illegal to be in the possession of controlled substances in the U.S. unless prescribed by a U.S. licensed Physician.
But you hit in on the head with "Distribution is supposed to be limited to the areas granted". Take "The Presitge" as an example -
- Released in the U.S. on blu-ray by Buena Vista
- Warner owns the distribution rights for the U.K. and choses to release it on HD DVD.
All perfectly legal, assuming nothing in the Distribution Agreement specified anything about format, which apparently was not.
IF Warner intentionally distributed copies of their U.K. HD DVD version outside the U.K., they would be in violation of the Agreement and could be sued. But they don't. They distribute to wholesalers and retailers in the U.K. If they in turn sell to U.S. residents and Exploited Cinema, it's not with Warner's knowledge and the wholesalers/retailers are not part of the Distribution Agreement between B.V & Warner, so aren't breaking any law. As long as the imported item is declared and any duties paid at port of entry, all perfectly legal. Not any different than me ordering a bunch of Brioni suites from an Italian retailer and importing them.
