Winter Cycling - up top rear pack for winter?

most of the pics i see of peoples winter rigs have them with packs on the top of their rear rack not the side.

Is that a winter balance thing or just coincedence?

It is more stable to keep the weight lower...

I'd say coincidence. Like electrik said, winter balance is even better with panniers (compared to carrying load on top of rack).

I'm just a rear rack trunk type of person. but yes: "the~higher~the~dryer" I also have a rain cover for my rack trunk

I prefer a rack trunk bag year 'round simply because it's less to drag through the headwinds, and I usually don't need more space than it provides.

When I need more capacity, then I add panniers.

"A bike is also an example of an inverted pendulum. Just as a broomstick is easier to balance than a pencil, a tall bike (with a high center of mass) can be easier to balance when ridden than a short one because its lean rate will be slower.[16] However, a rider can have the opposite impression of a bike when it is stationary. A top-heavy bike can require more effort to keep upright, when stopped in traffic for example, than a bike which is just as tall but with a lower center of mass. This is an example of a vertical second-class lever. A small force at the end of the lever, the seat or handlebars at the top of the bike, more easily moves a large mass if the mass is closer to the fulcrum, where the tires touch the ground. This is why touring cyclists are advised to carry loads low on a bike, and panniers hang down on either side of front and rear racks.[17]" (http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics#Lateral_dynamics)

In cold weather I don't need the change of clothes that I use in the summer. I use panniers in the summer.