Twitter treatment of URLs in tweets

After on and off experimenting with my twitter account for over a year, I stumbled upon a discovery today that I just had to share. I was reading an article on a tech site and at the bottom it gives you the option to share it with your social community friends. I clicked on the twitter icon, and was taken right to twitter and in the post box, there was the full URL of the page I was just on. I added a little note above it and submitted the post. I then noticed that in the post that everyone sees, the URL is shorted to a tinyurl.com URL. And here I thought all those other twitterers had tinyurl.com accounts and went through the trouble of making a reference first and then putting it in their twitter post. I think it's a cool feature and I appreciate it because I now have more characters to type. This is important when you only have 140.