I'm a gamer that's been importing for years. Generally there's 2 kinds of importers.
1) People who are really excited about a game and want to play it sooner, even though there's a version coming out in their language/country. Most of the people playing AC already fall in this category.
2) People who want to play certain games that will never or probably will never be released outside of a country that is not their own.
I fall under #2 almost exclusively. Most of the games I've imported, I did so because I thought it would never be released outside of Japan (or Europe, in the case of Last Window for DS - the only way to get that game in English). Occasionally I buy Japanese games for other reasons (I found the Japanese version for cheaper than I can get the US version, the US version has stuff cut out, etc) but mostly it's #2. Why? Because English is my first language. I'm learning Japanese, but I'm not super great at it. I have to use guides and/or ask for translation help from people I know who are good with Japanese. I can't get quite as immersed into games that aren't in my native language.
Thus, I'll be buying the US version of Animal Crossing New Leaf when it comes out, even though I live in Japan now and could easily walk down the street (literally) and buy a Japanese 3DS and the Japanese game.
However, I can definitely understand the appeal of buying a game you're excited about right away. Knowing that I could go buy the game right now is actually kind of hard. I really want to play it. But Japanese games are more expensive than US games (I get paid in US dollars still, so gotta deal with exchange rate) and there's that immersion issue for me. But some people don't mind as much for those things. Their excitement trumps all. If they are willing to spend the money and get through the Japanese (which, by the way, is not bad for AC since you don't need to learn/know any kanji), then it's totally worth it.
And, for what it's worth, I also can't say there's anything bad about buying both the Japanese and English versions if people are really into the game. The English version will have slightly different events and DLC and such from the Japanese version most likely. If you love the game a lot, you'll sometimes want multiple copies of it. So says the person who owns multiple versions of some games myself.