Function returns different value when called from ‘save_post’ than when called on page load

The “word_count” function below returns different values depending on where its called from. Why?

add_action('save_post', 'my_custom_save', 10, 2);

function myPlugin($post)
{
    global $rockScore;
    global $text;
    $text = strip_tags($post->post_content);
    echo word_count($post); //returns "350"
}

function word_count($post)
{
    global $text;
    $word_count = explode(' ', $text);
    $word_count = count($word_count);
return $word_count;
}

function my_custom_save($postID, $post){
    if (defined('DOING_AUTOSAVE') && DOING_AUTOSAVE) {
        return $postID;
    }
    else
    {
        if($parent_id = wp_is_post_revision($postID))
        {
        $postID = $parent_id;
        }
        echo word_count($post);die; //still returns "1"
    }
}

register_activation_hook(__FILE__, 'myPlugin');