If one wheel is stuck on ice, with an open transfer case and open diffs and no other form of traction control, all power would go to the wheel that spins the easiest, i.e. the one on the patch of ice, essentially resulting in 1WD. Stock Rovers overcome this problem with traction control, and the ability to lock the transfer case. On modified Rovers a common setup often includes air lockers on the diffs, or a Detroit locker in the rear axle and a Trutrack in the front to help overcome the problem with the open transfer case.

As for the rally cars such as the Subarus and Mitsubishis with AWD, they use a combination of electronic traction control systems and various mechanisms such as viscous couplings to help balance power to the wheels. WranglerDan seems to have a better grasp on which companies use which methods, so I will defer to him on that. One thing that you have to remember with the rally cars is that even though they are capable of driving on more off road terrain than a standard sedan, they are not an off road truck. They are also built with different intention. We go slow off road, take our time to pick a line, and work our way over an obstacle. The rally cars are built to go as fast as possible over uneven terrain. For a rally car, there is minimal concern about one wheel getting hung up on a slippery patch and getting stuck because they also have significant momentum behind them that will carry them over the slippery patch, and with their lower ground clearance than an off road truck, they are designed to go around the larger obstacles quickly than tackle them directly, so the AWD system works for them.

When you consider that the Rovers are also built more for the world market where off roading is a necessity rather than something you opt to do, the idea of having power delivered to all 4 wheels constantly while still being able to drive comfortably and somewhat reduce fuel consumption, the open center diff is a plus.

 

I did.

 

In most of the AWD cars, there is no transfer case as such. Just a centre diff. No low range. It seems complicated that there are so many different systems but its a case of horses for courses. If you just need a small car to get the groceries and live in a snowy, unmade road area, then something like a Subaru or Volvo AWD would be the best. I believe our Southernmost state of Tasmania has the highest registraion of Subies per capita in the world, and it's easy to see why. Rationally, Jeep Wranglers really are a waste of heavier duty 4WD hardware (and the extra fuel to drive it all along) for short urban trips on dry roads...can anyone say mall-crawler? They are however recognised as the best off-the-floor 4WDs for harder, steeper, deeper terrain. Then there are the modified machines such as those around here