As much as we may regret it, this really shouldn't come as a surprise. the normal pattern for Amazon would be to announce a big and noise public launch. At the very least there should have been a press release, not not just a quiet realization that the Appstore was open to the world.
This would have been an obvious move for Amazon, and while I thought it might be an accident I also hoped that Amazon would let it continue. Making the Appstore available outside the U.S. would have been the obvious next move for Amazon. This wouldn't just be to drive more traffic to the Appstore but also because of the upcoming Kindle tablet. More users would attract more developers and the more content that Amazon can offer users of such devices, the better to keep them using and buying the products.
P.S. I'm still waiting to hear back from Amazon on this. I will amend this post when I get a response.