All three editions do indeed have different covers - it's not that unusual to do that with updated editions of books. The third edition is a slightly smaller format than the first two and is printed on cheaper paper too. The first edition came out in 1995, second in 1998, third in 2003.
There's an odd editing error I spotted that only came up in the third edition. There's a photo in all three editions of Peter in 1968 wearing a striped rugby shirt - I'm sure we've all seen a number of photos of him wearing a rugby shirt around that time, he must have liked that look. But for some reason, the photo caption in the third edition changed "rugby shirt" to "ugly shirt" - guess the editors were style critics too!
