This isn’t an error with the book, but with the service used to view it:
The strikethrough for replaced code do not appear in the Kindle Cloud Reader. Tested on Chrome, Safari, and IE on both OSX El Capitan, Windows 8 and 10. The Kindle version looks great on my Kindle, but using the cloud reader trips me up quite often.
You could actually consider this a feature! The errors I get make me think through my code a bit more than usual.