Originally Posted by nobicus
In restricting my “ebook library” program to a connection only with Waterstones in the UK, Sony are in effect refusing to sell me books from their US website.
Yes, but they do this because the Sony ebooks are only licensed in the US. The same book can have a US and a UK publisher, and you can't (so far as I know) buy the US version of such a pbook in a UK bookstore either.
Amazon has the same problem with at least some of their Kindle ebooks, they are from US publishers with US but not worldwide rights. There are going to be angry posts about region-specific Kindle ebooks when the Kindle is available in other countries.
Other ebook vendors seem to get away with not checking the addresses on credit cards, but these vendors are not selling the reading device which may make a difference legally. I'm not sure what restrictions FictionWise places on EB-1150 secure IMPs though, so this may be a counter example.