Elite Beat Agents was for all intents and purposes a sequel to Osu! Tatakae! Ouendan -- new songs, vastly upgraded features, etc. And Ouendan fans in Japan are so crazy about the game that they're snapping up copies of EBA, even though it was produced for the US market. There are a couple stores in Tokyo that sell import games, but EBA is a special case -- it's being carried by most of the major retailers, none of whom actually carry American games. That they are all making an exception for EBA really says something. Even a tiny little family-run shop that I visit had EBA.
Oddly, even though prices vary a lot from store to store in Akihabara, Elite Beat Agents was exactly 4980 yen everywhere. I wonder where these stores are getting the game?