Considering each ski is attached to it's own leg, the only way to get them both to turn (via leg powered steering) is to turn each "independently" with the attached leg.
If both legs/skis turn the same amount, and the skis remain parallel through the entire turn, then hip socket rotation on the femur head that would leave the pelvis and skis pointing in different directions is not needed. In a parallel turn, the legs can work independently to turn their respective ski, without having to do the whole thing independently of the pelvis. In a wedge, if the wedge stays the same size, then also, no femur/hip joint rotation is needed.
The theory is that the two legs working in opposition to support the action of each. The old bar stools explanation. Well, yep, the process of that is very effective. But it doesn't HAVE TO involve femur/hip rotation. It still works if the pelvis goes along for the ride, and changes direction with the legs/feet/skis. As long as it does that, then little hip/femur joint rotation is going on. Yes, some has to happen, as the joint is not frozen, but not to the extent of creating any significant pelvic/feet directional orientation divergence. You CAN cause that divergence to happen, but you DON'T HAVE TO.
And one more thing to throw into this, which actually could be a thread of it's own. It's common belief that you can't steer on one foot. That both feet/skis need to be in contact with the snow for leg steering to be possible. Well,,, I'm here to tell you it's just not true. I can't yet explain the exact science behind why its not true (I have only a theory), I just know that in real life execution it's not. I have video of a turn in which the inside foot is held entirely off the snow, and ultra smooth leg steering is demonstrated from turn entry to turn completion,,, with no pushed or pivoted initiation,,, with no upper body rotary assistance,,, with no femur/hip socket rotation. Perhaps someone here would want to take a shot at how, against popular belief, it's possible.
RicB, you're probably right about the definitions factor. If one considers the "independent" referring to the each leg steering it's assigned ski, then femur/hip rotation is not needed to make it happen. If they reference "independent" to what the legs are doing, independent of what the pelvis is doing, and believe what pelvis and legs are doing (in regards to directional orientation) have to differ for ILS to exist, then that rotation is obviously necessary.
tdk6, keep in mind when trying to comprehend what is being said here: it's my understanding that those folks up in Canada define pivoting a bit differently then many others do. They consider steering to be a form of pivoting. It doesn't have to be that non-pressured redirection thing we see WC racers do at the start of a turn.