The United States changed version

As with Harry Potter and the Philosopher's Stone, the United States version of the novel has slightly changed text from the British version.

One particular section has been remarked upon, where the alteration makes the nature of Dumbledore's offer to Draco Malfoy before Snape kills Dumbledore in the Half-Blood Prince explicit.

The reason for the editing of the following text has not been explained on the author's webpage. The text can be found in chapter 27, "The Lightning-Struck Tower". The U.S. text was changed to match the UK version with the publication of the paperback edition. The parts added in the United States version have been highlighted in bold, below:

"[…] He told me to do it or he'll kill me. I've got no choice." "He cannot kill you if you are already dead. Come over to the right side Draco, and we can hide you more completely than you can possibly imagine. What is more, I can send members of the Order to your mother tonight to hide her likewise. Nobody would be surprised that you had died in your attempt to kill me — forgive me, but Lord Voldemort probably expects it. Nor would the Death Eaters be surprised that we had captured and killed your mother — it is what they would do themselves, after all. Your father is safe at the moment in Azkaban […]"