By The Way, I think the Renault Laguna 3 climate interface seems the best to achieve what you want:

http://www.flickr.com/photos/amcgore/2739241880/

You can modulate the rate at which it meets the setpoint through the soft & fast buttons, whilst in auto mode. That would be the best of both worlds.

The reality is that in a car, drivers don't care whether the cabin is 20 degrees or 21 degrees - all they care is whether it is too hot or too cold, and that they have fresh air...