WordPress.com is always adding new features and hadn’t even realized they added a related posts feature. The new feature called Possibly related posts was added back at the end of April. Here’s a brief overview on how this feature works:
In a feature we’re calling possibly related posts we’ll now try to show posts related to yours a little section at the end. If we find any posts on your blog that are related, we’ll put those at the very top and in bold. Next we’ll show other posts from around WordPress.com, and finally we’ll check if there’s anything in the mainstream media.