I guess where I struggle to grasp the whole white balance issue is when shooting something at a distance.
You are taking a portrait shot using an 85mm 1.8. Your D100 is on a tripod approximatel 12 ft away. Do you put the gray card where the subject will be and leave your camera on the tripod or do you take your camera off the tripod and move it closer and closer till you can fill the frame with the gray card?
You are shooting a landscape shot. What you are shooting is well over 1000 ft away. The lighting at 1000 ft away is certainly going to be different than 5 ft, 10 ft, etc. Where do you set up the gray card?