The new 4Runner has traction control too. All 4x4's will drive all 4 until a wheel loses traction. Then the net traction on an axle is the two times the traction of the wheel with the least. Traction control automatically brakes the wheel with less traction to redirect torque to the wheel with traction. A locking differential can redirect 100% of the torque so that a the wheel with the traction gets all of it. Traction control can't redirect 100% but does a pretty good job.

4Runners with the electric locking differential should only engage it when you lose (or will lose) traction. Leaving it engaged all the time is harder on the drivetrain, tires and axle seals not to mention increasing turning radius. Most times the locker is only needed for brief periods.

Though lockers are a great thing. They are not nearly as good as having 4WD. A TRD locked Tacoma Prerunner (2WD)doesn't stand a chance of keeping up with a open differential 4WD Tacoma. Having both the locker and 4WD is, of course, better. Having a second locker up front makes obstacles even easier.

The Jeep salesman obviously knows nothing about Toyotas which is why he is selling Jeeps.