This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
No difference in their compression format, just their purpose. An EAR is an enterprise application that may include a number of web applications, ejb applications etc. A WAR is specifically a web application. There are rules about how the contents of each should be structured in the JEE specification.