WW Wii Top 50 can give an idea of the situation:
http://vgchartz.com/worldtotals.php?console=Wii
Nintendo gets more than 70% of Top 50 sales.
Nintendo has two advantages nothing can eliminate except Nintendo itself committing suicide, the huge fan base of its established franchises and being first and having HW and SW carefully tailored to each other and heavily bundled, particularly when it releases new consoles and peripherals, like Balance Board with Wii Fit, Wii MotionPlus with Wii Sports Resort or Wii Sports with Wii itself.