Rationale for region lock-outs?

I've been reading about the Nintendo 3DS because I want to get one. I think it looks cool, except for this thing about not being able to play games from different regions. This never applied to me before, but I'm studying Japanese right now and may want to import a game at some point. The 3DS isn't the only thing that does this. DVD players and other game consoles also have lock-outs for different regions. But I really don't understand the rationale behind doing this, especially with game consoles. I can understand putting features in place to lock-out pirated or unlicensed games, but that's not the case here. It seems like that would only serve to prevent sales from people who don't live in a particular region. Nintendo is a business and I'm pretty sure they make a little bit of money for each game sold. This seems like it's only decreasing potential profits for everyone without giving any real positive benefit. Is there some positive benefit from a business side that I'm not seeing? I'm not happy whatever the reason is, but I just want to know what the thinking behind doing this is.