You guys are on the right track. The single resultant force vector (green arrow) displayed in the picture is simply a representation of the central effect of the all the forces acting on the entire body. In reality, there are an infinite number of resultant force vectors acting on each micro piece of body mass, each with the same (as green arrow) directional orientation.
Because their number is infinite, I like to describe it as a vector zone, and referring to the resultant force vector emerging from the body's Center of Mass (green arrow) is just a convenient way of representing the cumulative affect of that force zone on that body from the concept of a central point. It's not actually the reality, but it provides an excellent way of explaining balance.
Because the point we call the CM is the exact center of the zone, it represents the point of balance. If the body were completely rigid, and the force vector emerging from the CM and going to the ground was a stick, the body would balance perfectly on that stick. Any movement of mass from one side of the zone to the other would disrupt the state of balance, and the body would topple off the stick.
As long as the resultant force vector (green arrow) emerging from the CM intersects the ground somewhere within the skiers base of support (between the his/her feet) some form of balance exists and the skier will remain upright. If the resultant force vector intersects the ground outside of the base of support (outside the feet) balance is lost and the skier falls. Its really that simple.
The skier controls the ground intersection point of the resultant force vector (green arrow) via angulation. Because the angle of the resultant force vector (green arrow) is dictated by speed and turn shape, the only way a skier can control where that vector intersects the ground at any specific moment, during any specific turn, is by moving the location of his/her CM in relation to his/her base of support (feet). That's done by modifying the type and/or amount of angulation being used.
This is how a skier fine tunes his point of balance on the snow. When the resultant force vector ground intersection point (balance point) is somewhere between the feet, it can be adjusted toward the outside foot by increasing the amount of angulation, which moves the CM outside,,,, and it can be moved toward the inside foot by reducing the amount of angulation, which moves the CM inside.
Where the vector intersects the snow dictates the point of balance, and therefor the amount of pressure on each foot. a resultant force vector ground intersection point (balance point) exactly half way between the feet would result in equal pressure on each foot. The closer the vector intersection point (balance point) moves towards one foot the greater the pressure becomes biased on that foot. That is why we can tell that the resultant force vector ground intersection point (balance point) in the Herman picture is not directly under his outside foot, but is instead somewhere between his feet, very close to his outside foot. We know this by observing the amount of bend in each ski, and then assigning pressure levels to each foot according to those observations.
Finally, pressure levels can be artificially varied by extending or relaxing one leg. The problem is by doing so we are removing one foot from our base of support, which reduces the entirety of our base of support down to the width of the remaining single pressured foot. If we have not moved our CM in a manner that places the resultant force vectors ground intersection point directly under that remaining base of support (foot), the CM will begin an out of balance topple. We use that very principle to employ the external turn forces to disengage us from a completed turn.