Hi - thanks for the question! So the answer is no, we don't cover all the features of WebSphere in the book. We focus on the development of what we term "Modern" Web applications - meaning those that have RESTful back ends and front ends built using Hybrid Web technologies (JavaScript, JSON, etc.) As to differences between WAS and other app servers - I'm not going to go over that one - there is plenty of material on the internet to tell you that, and lots of helpful material on the IBM WebSphere web site.
http://www-03.ibm.com/software/products/en/appserv-was
Thanks!
Kyle