A thought... or two
Now that it seems Amazon is trying to close the loophole(s) that allow non U.S. Kindle owners to access the Kindle store... I'm wondering if this move supports the rumor of the UK Kindle release in the next week or so.
Maybe, Amazon is making bigger strides to open in more countries and must make sure those Kindle owners can only access their countries own Kindle store (those publishing rights restrictions come into play). T.hey will have to purchase a Kindle made for their country
As I recall, when the Sony Reader officially hit the UK, there was a slight variation in the firmware that would not allow those particular Readers to use the U.S. Sony store. The Readers can only use the official partners in the UK for Sony content (yes, I know content may also be purchased from other sources).
For those caught in this changeover, their Kindles will never be unusable because content can be purchased from other sources. Even if the content is not mobi, in most cases it can be converted for use on the Kindle. And as more and more ebook retailers are lowering their prices, not having access to the U.S. Kindle Store will be less of a loss.