Usage will always vary by locale, the same way grammar does, but again I raise my point about word processors using B, I, and U not just for styling text but giving meaning to text. For decades, it’s been dictated to us that if you’re going to cite the title of a book, it should be in italics. HTML should be the same way, ideally. Don’t ask the people to memorize a completely different tag for just the title of a book.