The subscriber stats show you all the users that have active email subscriptions to your blog using the built-in email notification system on WordPress.com. They don't include users that subscribed using a third-party subscription service or using RSS. Your site stats page displays how many followers you have, who your followers are, as well as how many people are subscribed to post comments on your site. Dashboard > Site stats < Totals, Followers, Shares and click the active links
Site followers: __ active followers
Comment followers: __followers, __following
Number of readers following your blog and blog posts comments.