Change this:
// This theme uses post thumbnails
add_theme_support( 'post-thumbnails', array('post', 'page') );
To this:
// This theme uses post thumbnails
add_theme_support( 'post-thumbnails' );
The problem is that the array is explicit, when used. So, post-thumbnail support will only be added to post-types included in the array.
Omit the array, in order to add Theme support for post thumbnails universally.