Well, first off, when you're talking about the inside ski ahead of the outside ski, if you were simply shuffling the skis back and forth, like walking, movement could be described in the sagittal plane, but looking at total body movement through several turns, the inside and outside body halves are exchanging leads, which can be seen as rotation through the transverse plane:
In any case, what you are saying is correct, the inside and outside halves should align up and down the stack with the skis. However, it's not the case where anyone with any knowledge of skiing or biomechanics is saying that inside ski lead should be eliminated. I defy you to make complete turns on a medium to steep pitch with any kind of speed without having the inside half of the body leading the outside half. More to the point is that in a completely "square" postion, there is very little ability to articulate with hips and knees. Nevertheless, unlocking these joints does not require much in the way of lead change. A rule of thumb I personally like is to not let the toe of the outside foot retard behind much farther than the arch of the inside foot, so a few inches is all it takes, and consequently, every body part on the outside half in relation to its corresponding body part on the inside half should "ideally" create the same angle when looked at from above. Having said all that, there are some observable differences seen among racers from different federations. The Swiss for example, typically display a bit more inside lead than the Austrians for example. Compare the picture of Cuche with that of the Austrian Gruber:
While Gruber is much more "square" than Cuche, there is still a small amount of inside/outside lead observed.
The point is, there are a wide range of body makeups, strength capacities, ranges of motion and history of training and instruction in all top level skiers, not to mention the feel of and responsiveness of different skis. Within reasonable boundaries skiers are trying to find the movement patterns that work best for them in varied conditions. Don't get sucked into some dogmatic philosophy. It's a matter of developing athletes, not robots.