Yes, you're right that with an ordinary (so-called) open differential, one wheel sometimes gets all the torque output from the engine (the myth of the so-called "drive wheel"), but that's noticeable only when there is wheel slippage (loss of traction). And that's when the popular myth that only one wheel gets the "power" got started -- it's observation resulting in a belief, but based on inadequate information resulting in an incorrect conclusion.

To understand the differential, think of not having a differential. On my old 4WD SUV, I could lock the rear differential (thus no differential action), and then both wheels are joined together and spin as one so that their rotational speeds are identical (like a child's toy car with the wheels mounted on an axle) with torque is going equally to both wheels -- and this isn't affected by the amount of traction of one wheel or another. In fact, one wheel could be off the ground, up in the air (zero traction), and while that raised wheel is just turning exactly as fast (or slow) as the other, that other wheel will still push the car forward. Of course, it would be very bad if I drove on a paved, clean road (i.e., with both wheels having good traction) with my differential locked -- each wheel would try to turn at different speeds on a curve, and would probably break their axles.

A differential actually delivers some torque to both wheels, not just one, assuming that they have equal traction and no other factors that complicate the situation. But sometimes only one wheel gets almost all the torque (when there's wheelspin) -- so, which one? There is no absolute answer.

For example, if you had a "hot rod" (e.g., if you're old enough, think GTO or something similar), where there's so much torque that the turning driveshaft can literally twist or rotate the rear axle so that it presses down the left rear wheel and lifts the right one, you'd get wheelspin from that lifted right wheel -- less weight on it, and it breaks loose and spins. That's why limited slip differentials were popular with those owners, because it would divert some torque to both rear wheels, and the car would accelerate better because both rear wheels were pushing it forward.

However, you don't have to be concerned with excessive driveshaft torque. You're concern is traction. If both rear wheels have good traction, both get power from the engine and will push the car forwards. If one has so much less traction that it's able to break loose and spin, then all the torque will go to that wheel (differential action) and none to the wheel with more traction, so the car will have one spinning wheel but will not progress forward (because the wheel with more traction but with less torque doesn't get enough to propel the car). This observation is probably an example of how the myth (of one driving wheel) was started -- people saw that one spinning wheel and thought, "that must be the one that's the driven wheel."

But because there are no "driveshaft torque" effects on the 240, whichever wheel spins depends on which wheel has the least traction. You should want to ensure that the wheels on BOTH sides of your car have equal traction! And enough of it -- it's not impossible, and despite also improbable, that you might wind up with both wheels spinning, and your car would be stuck nevertheless, if they're both on, e.g., glare ice.