I spent a good deal of effort on the issue of Amazon locales for my book web app. There are quite a few reasons for this:

* Some books will exist in one locale but not in others;

* Some books will be in stock in a locale but not in others;

* Some books will have a different cover and/or slightly different edition if it's a UK or USA version;

* If you are buying the Kindle version, availability varies by country, but only UK residents can buy from the UK Kindle store.

* If you buy many books from the States and you live in the UK, you'll end up paying hefty import charges.

* Delivery from your closest Amazon is usually faster (provided the books are in stock) and free (or cheaper for expedite shipment).

If you go to the Staff Picks of the Week section of my site (http://anynewbooks.com/staff-picks/), you'll notice how under each book I'm forced to place up to 5 links (US, Canada, UK, Kindle international, UK Kindle). It may be slightly confusing, but in my experience international readers appreciate the effort (the rest of the world is quite sick of US only web apps to be frank).