Official Xbox.com Forums:
The beta MAY not be restricted to the US after all.http://www.cod4forums.com/index.php?showtopic=146
Here is the entire quote.
QUOTE(IW Communications Manager)
I wanted to give some clarity on why the Xbox 360 beta is US Exclusive. While we would have loved to offer the beta across all platforms, world-wide, with an unlimited number of members, we regretfully have our limitations due to our development schedule and resources.
In the interest of time, resources and availability, we had to concentrate the beta's focus. The team is also crunching on a PC demo, to follow the console beta, which will be available worldwide.
Ok after a few mins after releasing this anonucement 402 has took it all down and replaced it with this awesome news:
I know there has been an uproar regarding the fact that the Public Beta may be restricted only to US residents. I wanted to give you guys an update and let you know that this is currently an unconfirmed statement, as details on Beta limitations are still in the works.
I will update you PERSONALLY when we have an official confirmation on Beta Limitations so bare with me while I get this all sorted out for you guys.
More info coming soon."