I have no idea why the titles are sometimes changed; 'Ripe' was particularly unfortunate because Cheryl Sternman Rule, a US writer, had a cookbook out at the same time with that title [also about fruit].
But Appetite is not an example of the phenomenon; it's the same title as the UK edition: Appetite: What Do You Want to Eat Today? The US version of the second volume of the Kitchen Diaries is, as far as I know, not yet out, but I assume (and hope) it will also be called Kitchen Diaries II.