I remember noticing that too, and so did my racist girlfriend.
Bear in mind that it was allowed to be racist in those days, so please don't blame her. I remember her delight when she found a Little Black Sambo book in a jumble sale. She bought it, and used to read out passages from it, which were so bad that they were forbidden even then. I can remember some quotes from it, but if I were to reproduce them here, I'd have the police knocking at my door.
Little Black Sambo was a prescribed book for primary school reading when I was learning to read. I can still remember the story about when he turned the tigers to butter. I think that book came after "Janet and John", which is probably also illegal these days. It had phrases like, "Look John, look. See the ball, John. See the ball" and "One, two, three. Three little kittens. See the kittens in the basket. See the kittens play in the basket". Anybody remember it? Absolutely shameful!