Amazon USA warns foreign purchasers of potential incompatibility problems (emphasis in original):
Global region codes identify specific DVDs that are compatible with the players typically sold in that region. The majority of all current titles play in only one region unless otherwise noted.
Most of the DVDs sold by Amazon.com are encoded for Region 1 (for standard DVDs) or Region A (for Blu-Ray DVDs) only and may not work on DVD players in other countries.
This does not stop importers having a big sad when discs won't play:
Feeling guilty about regularly acquiring her TV and movies through other means, a friend of mine recently ordered some blu-ray movies from Amazon. When they arrived in Australia she discovered that some of them are blocked from playing here. There’s nothing wrong with her equipment: it’s just that the publishers have deliberately crippled their discs so that if someone in Australia tries to play them, they will not work.
Boo hoo hoo. Back in the bad old days -- the 1980s -- I paid around $2,000 for a video machine capable of playing both NTSC (USA) and PAL (Australia) videos. Life's a bitch, ain't it?