When movie studios distribute movies on they have different region encoding.
Example, there is one way of encoding them for distrubtion in the US, another for Germany, another for Asia, etc.
It sucks because a studio might release a movie with a ton of extras in Japan, yet release a barebones edition here in the US.
I order a lot of movies from yesasia.com and would get frustrated by them not having a copy in Region 1(North America) of a movie I really wanted, so I broke down and bought a region-free DVD player. The first one was garbage, but the second one has been great.
It's similar to the different encoding types for video cassettes. In North America, it's NTSC format while in Europe (and I think Asia) it's PAL format. Not sure of other countries, whether they are NTSC or PAL.