I don't get why they do this, either. I still don't understand why there are two different titles for the first book of the Peter Grant series: Midnight Riot in the US, The Rivers of London in the UK.
Different covers are terrible some times as well. I especially hate it when, in the Netherlands, they switch mid-series with which version (UK/US) they sell. I want the complete series in one edition. Is that too much to ask?
The worst of all is when books are split in the US, but not in AUS/UK, like with Isobelle Carmody's Obernewtyn Chronicles. Australia's book 5 (The Stone Key) is published as books 5/6 (Wavesong and The Stone Key) in the US and Australia's book 6 (The Sending) is published as books 7/8 (The Sending and The Waking Dragon) in the US, which made it very difficult when I was buying the series, I had to be sure that I was buying the correct book (because you can sometimes buy a US edition of a book here in Australia).
Yes, that must be confusing as hell! Some editions (I don't know if that's country related as well, I don't always check) of ASOIAF are also sometimes split and other times not, and more recently I think they split the new Gabaldon in Dutch but not in English...
On one of my Dutch book forums we've got a saying for this king of thing, is roughly translates as 'Publishers are weird' because they often make choices none of us understands...
On one of my Dutch book forums we've got a saying for this king of thing, is roughly translates as 'Publishers are weird' because they often make choices none of us understands...