Why do British books in other English-speaking countries have different names?
It is sometimes a question of lingual differences – not every “English” word has the the same meaning in English speaking countries (American and British English display an enormous gulf in some respects). Additionally it is a question of what would be understood better. When the James Bond film “Licence to Kill” came out, it was to have been titled “Licence Revoked” but a survey in the States showed that very few Americans knew what the word revoked means.
Basically as harsh as it sounds nations such as America need things dumming down for them, if you published a book called the Philosopher’s Stone they wouldn’t have the faintest idea what the book was about so they wouldn’t buy it. But if you publish it under the name of the Sorcerer’s Stone this tells your average American that the book is about magic, which will appeal to certain people. So basically American books need a title that gives your average American an indication of its content, while the more scholarly British can divulge that if it a Philosopher’s stone is involved its sure to have magical properties.
