Philosopher's in the UK
Sorcerer's in the US
Marketing is given as the reason for the difference "The simple fact of the matter is that American publishers think that the word "sorcerer" sounds more enticing and magical than the word "philosopher." At the time, the belief is that American kids would have more familiarity with the term "sorcerer" than they would "philosopher", therefore, making it more likely for them to pick up the book at the store."