Also rip offs of other games.
We don't need nine skyrims now do we?
You realize this has been true since forever? Game is popular, other devs try to cash in on the success by making ripoffs. Existed even back in the NES days and even before then. This isn't even true to video games. This is life in general.
(http://www.blogcdn.com/www.joystiq.com/media/2008/12/giana.sisters.box.490.jpg)