Ok, so apparently the reason  I can buy physical books from, say, waterstones.co.uk, and not ebooks is because, when I buy physical books, the place of sales is Waterstone’s servers (ie in the UK), and they then ship it to me (incurring import taxes and whatnot). When I buy ebooks, the place of purchase is my computer–which is firmly in France, where Waterstone’s isn’t licensed to sell English books per their agreement with the publishers. But of course, no one but the UK resellers are authorised to sell UK editions…
*goes bang head against wall*
Why am I suddenly reminded of Kafka here?
I have no idea whether it’s true, but I wouldn’t be surprised.