There's a bit of a difference there, actually. It's one of those differences between physical and electronic media that points out how silly it is to try to impose the same restrictions on both.
I'm not a lawyer or anything, and I'm in the USA on top of that. But copyright laws are more or less standardized by treaty in the important respects.
As far as I know, it is legal for
consumers to import foreign goods for their own personal use, even when those goods are already licensed in their locality. It is
not legal to import and sell those goods commercially.
For instance, Disney holds the American license on a lot of Jackie Chan movies, which they choose to release edited and dubbed-only. The American Hong Kong DVD importer Poker Industries is enjoined from importing and selling the original uncut versions of those titles because Disney has the rights in America. But it's perfectly legal for individual Americans to order the original Hong Kong versions of the movies (which are conveniently subtitled in (usually poor) English) directly from Hong Kong export shops for overseas shipment.
(This is why the whole system of region-locking was implemented in the DVD standard—Hollywood trying an end run around the perfectly legal practice of consumer importing. Fortunately, it was largely ignored by a lot of DVD player manufacturers)
With Internet e-goods, the border between import and local sales are blurred, because a website can deliver those e-goods to people in its own country or halfway around the world with the same ease. But it is still bound by local laws. That's why Internet radio service
Pandora only allows access to people in the USA—they would have to pay British royalty rates for listeners in the UK, even though they are located in the USA.
If ebook.com does not have the British sale rights for books, then they are not legally able to sell them to Britons. If Fictionwise is selling them, either they do have the sale rights or else they are banking on nobody caring enough to sue them. (If so, then it's not the only thing that Fictionwise/eReader do that they're not supposed to; the whole minimum-purchase-or-service-fee-by-credit-card thing that they do for micropay is in abeyance of credit card company rules.)