Another very important reason skid steer "trumps" any car-like driving method is that skid steer keeps the middle of the machine open for game functions. For example, in 2010 it would have been difficult to make a kicker work around this or in 2009 or 2006 it would have been more difficult to pick up balls from the ground. The front-middle of the robot is prime robot real estate.
Plus that whole thing with it being more complex and less manuverable.
Regards,Bryan