I believe it's not the content options, as one unreliable source has claimed, because the new Kindle Fire HD is launching in Europe within a reasonable time frame. No, the issue is likely a simple matter of supply and demand. It is my guess that Amazon is limiting the Kindle Paperwhite to the US because they want to make sure they have enough. And if you've been tracking the delivery dates for the KPW, you'll see that I could be right.
I ordered my KPW on the Friday after it was announced. My expected ship date is 16 October - a little over a month away. If you check the listing for the KPW, you'll see that the current expected ship date is now 22 October. While a shift of 6 days isn't terribly large, it does show that Amazon was right to be cautious about the supply issue. Had the KPW been available to the entire world, it would likely be backed up for several weeks (if not a couple months), not one.
To be honest, I don't know if this is a demand issue or supply issue, but clearly Amazon is having the enjoyable problem of making sure they have enough KPW to sell. And luckily for the international buyers, this problem will eventually go away.
I would half expect that the KPW will go international some time in late November. I don't expect the supply bottleneck to last, and the current high demand is at least partially due to customers buying the KPW to ship to friends overseas.
In any case, the rest of the world will only be a couple months behind the US. That is a far better situation than with the Kindle Touch, which didn't go international for a good 6 months.
via The Bookseller (paywalled, so don't bother clicking on it)