OK but when you say it won't be "unlocked" in japan, you mean "unlocked" as in not going to be possible to activate it there if the game is bought somewhere else, or "unlocked" as in you won't be able to play it in japan even if you bought it and activated it somewhere else?

Both.
Basically, if you pre-ordered it in say the US and moved to Japan before release, it will forever state "Unreleased" it will never unlock.
If then go back to the US and run Steam, it will unlock and activate (as tested by the affected user who used a VPN/proxy to spoof a US IP for the Steam client).
However, even once unlocked and activated with a US IP, once you switch back to your Japanese IP the game will no longer launch (it even returns to "unreleased" on the games list).

I require evidence to support this claim, because if this is true It might very well be my first major gripe with steam. And no, speculation on an internet forum won't be considered evidence.

From what I've read it seems to be a problem created by EA Japan, not steam, but I still hope the game unlocks after all the other regions have unlocked. But if not a guess I can draw a conclusion:
Don't buy EA Games EVER, specially through steam.

Well it looks like everything goes downhill.
Game prices guing up while content getting chopped out for being sold later as DLC.
Regional restrictions, that made me resign from buing all games with GfWL tag on them.
I use Steam only for their discount offers, and not all of them because of pricing policy for europe most of them are still more expensive than retail.
So it seems that for me any new games got to get old before i'll buy them.

The difference is Steam's gatekeeper behavior, and the associated fact that they reserve the right to take back your games at any time.

Impulse, GFWL, GamersGate, D2D etc can all take back your game at any time too you know?

I don't know about the others, but I've bought a few DRM-free indie games from D2D. Do indie games in Steam DRM-free too?

I think if the publisher did not put DRM on the game Steam does not add any additional DRM other than the DRM of the Steam service itself.

This is very unlikely to be an EA Japan decision. Based on responses I've had from them in the past when I've mailed them (actual letter, not email) EA Japan basically couldn't care less about Steam -- they have no current plans to use it, nor to block access to games being played over it in Japan.
As far as DA:O concerns, EA Japan aren't even interested in publishing it. And if they're not interested in publishing it; they certainly aren't going to be asking a DD service they have no interest in using to suddenly block access to a game being sold on it in a language that they only support as an after thought.
And besides this, the more important point here is that no publisher can seriously expect to be able to dictate how a game is handled when it's not even sold in their region. Thus EA Japan can in no way expect to be able to block access to a game sold by EA in America when the purchaser just happens to suddenly visit Japan for a holiday/is bought by a Japanese visiting the US and then taken home to Japan.
And certainly not without an adequate warning displayed before purchase -- of which there is none.

the difference with Impulse is that if they invalidate your key, you can still play the game locally.

Impulse will not take back games without offering a refund, I have no idea about GG or WL, and D2D has the future download of purchased games specifically as part of the purchase price, so they can't either. Also, none of the clientless services can "take back" games you have already installed.

Can't speak with regards to GFWL as I've avoided it like the plague for other reasons, but Impulse, GamersGate, and D2D, while they certainly do have the power to stop activating games at any time, can only prevent a game from being installed. With the exception of multiplayer games that operate through servers under the control of those services, once a game is installed it can be played without ever having to contact the Impulse/GamersGate/D2D servers. In contrast, if Steam decides to cut off access to a game the effect is felt the moment you next try to play the game. Offline mode might mitigate this a bit, although from what I've heard the extent to which it works varies quite a bit game to game.