*** THE BALANCING "ACT" ***
Good posts, Mosh--and a great topic starter! I agree with your conclusions, but here's something to consider:
The inner ear does not really respond to "vertical"! It senses only acceleration. Think of the disorientation we experience in total whiteout conditions, and the dire consequences pilots talk of when flying without visual references. Gravity still operates in these situations, but what we lack is a VISUAL reference to "vertical" (or horizontal), and a visual reference to speed.
The inner ear's three "semi-circular canals" roughly representing three axes of rotation, sense "angular acceleration" (rotational movement). Other components of the inner ear sense linear acceleration, and can indeed sense "gravity," but only when there is no linear acceleration. (Here
is a somewhat technical web site for more information). Combined with a VISUAL reference to horizontal and speed, the effect is as you say--our bodies tend to want to be "upright."
The good thing about this is that any kinesthetic sense of "upright" that we possess helps us maintain balance even under circumstances where "balance" does not mean "vertical." When leaning into a turn (which is a form of acceleration), or speeding up or hitting the brakes, these acceleration sensors help us adjust "balance" accordingly--if we let them!
So vision plays a very big role in balance too. And the visual and inner ear senses must, in a sense, "agree." I recall reading, a few years back, about a high-speed train somewhere in Europe, where the cars actually tilted as the train turned, simulating a banked turn so that, for example, drinks wouldn't go flying off trays when the train turned. Apparently, they had to reduce the tilting action slightly because it was making passengers ill. Their eyes saw that they were turning, but their kinesthetic inner-ear senses didn't match what their eyes were telling them, and people actually got sick! Interesting....
So balance is very complicated. Vision, along with the inner ear, and other kinesthetic awareness (pole drag, for example), combine with experience and trained, learned "balancing movements" to create what we simply call "balance."
It's interesting to note, too, that in at least some ways, we are NOT balanced on skis, at least while we're turning. If balance refers to some sort of "equilibrium" of the forces acting on us, then by definition, turning skiers cannot be in balance! Or--balanced skiers cannot turn!
Turns represent acceleration. Acceleration can only result from "net" or "unbalanced" forces acting on us. The physics definition of "balance" is "The state of a body or physical system at rest or in unaccelerated motion in which the resultant of all forces acting on it is zero and the sum of all torques about any axis is zero" (American Heritage Dictionary). A turning "body" is NOT at rest or in unaccelerated motion!
Who cares, you might reasonably well ask? Well, it's important in this respect: What we call "balance" really becomes simply the ACT of dealing with all the changing forces of skiing so that we maintain an effective stance, control pressure on the skis accurately, and don't fall down!
Clearly, these are things we can improve at!