According to The Bookseller's Graeme Neill, Waterstone's has roughly 7,000 ebooks on the website and aims to have 20,000 titles online by the end of the year. I agree about the website, it's a pain to look anything up on there. I know a lot of W's employees who use Amazon as a reference site instead their own company's... Atlantic Books published Anathem in the UK and, for some reason, they didn't make it available as an ebook. That it's available in the US, has nothing to do with this (and certainly isn't any bookshop's fault), because the US rights lie with Harper Collins.