This is an update from an earlier post (http://justanotherlearner.blogspot.in/2014/08/facebook-bug-maybe-maybe-not.html) where I had misunderstood a feature of FB and pointed it out to be a bug.
Today, I came across the facebook privacy page (https://www.facebook.com/about/privacy/your-info#public-info)  where it is written that

"Your name, profile pictures, cover photos, gender, networks, username and User ID are treated just like information you choose to make public"



So, it is absolutely fine if you are able to download the profile pictures of others. However, FB still provides the option of keeping your profile picture private . There is certainly a discrepancy in information and it should be resolved.