I think that the XBox 360's region protection (term used loosely) is entirely an option on the part of the publisher. If the publisher wants to include region lockout, he's free to do it. If he doesn't care, then he can leave the disc without lockout.
This is second-hand information, though. My friend was saying he could play American games on his Japanese 360 since apparently Americans don't care. The Japanese games he tried on another of my friend's American XBox didn't work. I guess they're still more traditional?
A ton of American games work on the Japanese Xbox (there are a few that don't, but...the ones that work far outweigh the ones that don't). I think American game publishers just care a lot less XD The opposite goes for Japanese games.
I didn't know that there were restrictions -within- the restrictions, though. Guess I'll hold off on an Asian version of iM@S2 just in case...
(well, hold off on it further XD Since I want some iCOMU-M@STER cheats for it, first, as well)