It's a genuine offer, but for UK-based buyers (and those who can appear based in the UK) only: the version they're seeing on Amazon.com is the UK one, listed for whatever reason on the US site but available there solely to UK buyers. There are other books like this; the Rod Rees series mentioned the other day, for example. US-based members will often have trouble even finding the item pages for these editions, and if they do there'll be a "This title is not currently available for purchase" message where the buy button would be. Here, for example, is the page for the UK edition of the last Demi-Monde book, which doesn't even have a US e-edition yet:
http://www.amazon.com/The-Demi-Monde.../dp/B00CUE0DD8.