[Beav]

Fog is always created by warm, moist air being condensed by cooling. Until the air inside the car is brought to relatively the same temp and humidity the fog will be noticeable, that's why it tapers off instead of instantly disappearing. Notice that I didn't say that it was the cool air in the system hitting the warm ambient cabin air. Sometimes it's exactly the opposite and the fog quickly dissapates compared to other times when the cabin air is warmer.

We have the same issues on this side of the pond, I get about fifteen to twenty similar complaints each season. The reason it's more noticeable on newer (and smaller) cars is that the evaporators are made smaller to fit better. The result is that they drop the cabin to the same temperature but they do it by cooling a smaller volume of air much more quickly. This creates a larger temperature differential and the fog is more noticeable. Older cars had larger evaporators and cooled a larger volume of air to the same temp, just more slowly and with less temp differences.