The book is fairly concise and inexpensive, particularly in its paperback
version.
It is accessible, rich in graphics and published by one of the world's leading
scientific publisher (Routledge).
We would like to believe that it is one of the best source of background
information on the subject.
The companion site is continuously updated with new and improved material.
Using it in conjunction with the book, particularly in an educational setting,
creates multiplying effects. So, you get more than a book, you get a complete
online support structure which helps avoid obsolescence.
If you are an educator and in the past the site saved you countless hours
of preparation time, now it is time to show your appreciation. You may also
consider adopting the book as required reading for your classes.
The same applies if you are using this site to get background material for
your research.
In a market economy, buying is the best signal one can send about the relevance
and usefulness of a product.