magusgs - Microsoft advocates publishers to region lock their games, but it's not for them to make those calls. In the end, it's up to the publishers to decide what they want to do in regards to region compatibility.
InfiniteNine - Yes, it's true that there are many games that work for both U.S. and Japanese 360s, but many of those games share a universal build, including BlazBlue. To put it short: Both the Japanese and the Americans got the exact same game; they were just packaged differently.
If you play around with your machine's and the game's region and language settings, you can see that they are exactly the same game. I can vouche this for BB because I imported the Japanese release for PS3 and I was able to switch even the credits to Aksys just by changing the language settings to English.
This American release of Agarest Wars, however, is intended specifically for the U.S. market and I was informed that there is no Japanese text. So it's a different build for sure.
In the end, it's pretty much up to Aksys what they do with the game. But if there is demand for the game in Japan, I don't see any reason not to make it region free. There aren't too many cases where Japanese gamers want to reverse-import titles.