It's no longer "customary" in the U.S. either, at least not universally. As I've already said, Chicago Manual of Style (produced by the University of Chicago Press, which publishes primarily books) suggests 's in all cases except Jesus' and Moses'. Many editors here use that book as their primary style reference.

Many other editors (primarily journalistic ones) follow the Associated Press Stylebook guidelines. I've just checked those and found that the AP Stylebook (primarily intended to be used by the press) advocates the use of the apostrophe without a final s for all proper names. So I'd venture it's more "customary" in journalism than in scholarly English...yet another reason not to believe everything you read in the newspaper!

Claire