Difference between International edition of a book and a non international one
International editions are cheaper

They are sold cheaper, in English speaking countries (or countries with education in English) outside North America: India, China, etc. The content is equal to that of US/North American versions.

There are two reasons why they are cheaper:


because they are printed in cheaper version: paperback instead of hardcover, sometimes black and white
because the publisher knows he cannot sell them at their US price anyway, so they are willing to sell them at the price people will buy them (better to sell them cheaply than not at all)


Sources:


http://www.thetextbookguru.com/2011/04/20/international-textbook-editions-a-cheaper-alternative-2/
http://www.abebooks.com/books/Textbooks/international-editions.shtml
http://answers.yahoo.com/question/index?qid=20080825164810AAGRN80


There was also a case about import of international edition textbooks in the US supreme court last year (http://arstechnica.com/tech-policy/2013/03/thai-student-protected-by-first-sale-supreme-court-rules/).