Douglas Adams' American publishers forced him to change some of the text in Life, the Universe and Everything: "Asshole" became "kneebiter", "shit" became "swut", and most bizarre and hilarious of all, "fuck" became "Belgium".
According to Adams, because kids were reading it
As recounted in Hitchhiker's Guide, by M.J. Simpson:
"I think what happened was my U.S. publisher was unhappy about using the word "fuck" because of the number of kids who read the books," explained Adams later. "I was a bit frustrated by that, but then it gave me an idea and I put in the whole Belgium piece."
Of course, this was merely the author's impression of what his publishers wanted, not a statement from the publisher itself.
I was unable to find any direct statement from the publishers.