A) You travel to a nation with no recognition of US copyright law. There, you purchase a pirate DVD, which, in that nation, is 100% legal. You then fly back to the US with it in your possession. Have you broken the law?
B) You buy space on a webhost located in a similar nation, with no respect for US copyright. You create, on that server, a bittorrent tracker explicitly for pirated material. You advertise it all about the web, and it generates a large user base. You maintain it, even generate ad revenue from it, but not one single bit comes back from that server to your box. You never download anything from your own server, aside from basic maintainance. All the copyrighted material resides in East Timfuckrealistan, where that material is illegal. If it enters the United States, it's through someone elses computer. Have you broken the law?