It is important to distinguish the positions of ice dancers from those of freestylers. Don't try to learn good ice dance posture from freestylers, and vice-versa. And recognize that not all coaches and all skaters are the same, even if you just watch the people who win medals on TV.
I think isolating motions to the leg/hip joint and below is mostly an Ice Dance (and Ballroom Dance) affectation. (And even so is often dropped in Free Dance).
Anyone can tell by watching TV that most freestylers do lean forwards, and I think they bend at the waist. Maybe it gives them a stronger sideways push and pull on backwards crossovers, and in some cases stronger jumps? I can't quite figure it out, but it is obvious that the isolation restricts the body's ability to use some of it's strongest core muscles.
AFAICT by watching the best skaters on TV, Ice Dancers lean forwards too, when skating forwards, because it is more efficient. But the bend is at the leg/hip joint and below, not higher up at the waist.
When I took an ice dance class with a high class coach, he spent a lot of time emphasizing the idea of letting the body above the leg/hip joint move as a unit - i.e., it had virtually no internal motion. Not just bends. In his style, rotations occur almost exclusively in the hip/leg joint, and a little in the ankle. I found this completely unnatural, very hard to do, and very inefficient. I sent an inquiry to an ice dance mailing list, and was told this is a common style.
On the other hand, when I took ice dance lessons from another coach, he was constantly counter-rotating the waist and the lower body from each other. For example, if he did alternating cross steps, skating in alternating arcs, the upper body maintained an orientation directly facing the far wall at all times, though the legs and knees below the hip joint rotated around to match the skating trajectory to face the other walls during the motion.
Both of those ice dance coaches had very impressive competitive records. Both were Russians, BTW. And neither bent forwards at the waist, as far as I could tell.