Yes you are right, the image on the website could be better.
However, the image for the book cover was much higher resolution at 2550 x 3300
pixels (8.5" x 11" @ 300dpi) and the level of anti-aliasing looked fine too. I
have a physical copy of the book (8.5" x 11") and there aren't any anti-aliasing
artifacts that I can see.