If we think of your website as a gallery of pictures, it would be nice for you to have some pictures in it, but there are many ways to make a gallery in your site. You can make a video of your website, or you can make a slideshow of the pictures you see, or you can create a whole series of pictures, some of which are beautiful, some of which are ugly.
This is a good thing as people don’t need to be in the middle of a life-changing web page. It only makes the web world easier to understand. The web is more complex, but it’s not tied to a particular language. So it’s likely that the author/editor of this book will be able to do something similar in other languages because they use the same platform.