No Strings Attached To Friends with Benefits

Would someone please tell me the difference between No Strings Attached and Friends with Benefits? At first I thought they were the same movie. Then, I wondered why Mila Kunis was doing two movies with the same storyline. Then I realized No Strings Attached starred Kunis' Black Swan costar Nathalie Portman.

No Strings Attached plot summary:
A guy and girl try to keep their relationship strictly physical, but it's not long before they learn that they want something more. (Stars Natalie Portman, Ashton Kutcher)

Friends with Benefits plot summary:
Dylan and Jamie discover that adding the act of sex to their friendship does lead to complications. (Stars Mila Kunis, Justin Timberlake)

No String Attached

Friends With Benefits

Then I realized that No Strings Attached and Friends with Benefits were the same movie as Black Swan, except Black Swan didn't have those guys that got in the way and I was able to focus on Portman and Kunis. I didn't actually see Black Swan. Or the other movies. But, I did look at the movie posters.

Black Swan

Edit: And then a couple weeks later I found out I was not the only one who had this idea. Or perhaps the producer of the following video came up with the idea after seeing my post.