There are system selling games, but system selling games don't work (and have never worked) like many people expect them to ...
When most people talk about system selling games they're expecting a game release to have a very large initial boost to hardware sales, with a noticeable sustained boost from then on. It is not unusual to hear claims from people that the release of a game (like Final Fantasy XIII) will cause millions of people in one region to buy a system.
How system sellers actually work is that when a game is announced for a system (exclusive or not) people will factor in the release of that game into how appealing a console is, and for months/years in advance there can be a slight boost in hardware sales. Upon the release of the game there is an initial hardware boost but it is almost never as big as people expect, and soon after the release of game (a couple of months) if there isn't a new "System Selling" game on the horizon sales of the console will actually be reduced.
