On his blog, Brian Keaney, a UK author, explains to a reader why his books come out so much later in the US than the UK:

“They come out later in the US because I am a UK writer and I write them for my publisher over here. They then sell them to foreign publishers, inlcuding those in the US, who slot them into their publishing schedule at a point that suits them. In the case of US publishers, there is a further delay while the book is re-edited for the US market. This means that UK terms like trousers, trainers, jumper and petrol get changed to US terms like pants, sneakers, sweater and gas. Interestingly, when a book by a US author is published in the UK the UK publishers don’t bother to Anglicise it; they just assume (correctly) that the public will be able to work it out for themselves.”