Rear Air Vents : Blow cold air only.....why?

I have the rear air vents, it's winter over here, and while it does'nt bother me directly (as i rarely carry rear passengers), i was just wondering if anyone can work out why the rear air vents only blow cold air when the front is being warmed?
If these vents are just piped through from the front, why would'nt they just blow the same air thats been warmed for the front? Can someone please give a logical and technical reason for this, as i just can't work it out? cheers

I don't know the reason but it has been discussed on here a few times now, I know my occasional passengers have commented on the rear being cold.

Yeah i remember seeing the discussions in the past (tried finding them through the search,but could'nt locate them) and i don't recall anyone finding out why they only blow cold air,when logic would suggest that if you pipe air through from the front,then it should be as simple as being the same climate controled air.

http://babyrr.com/forum/Thread-Cold-in-t...ight=Cold.

Thanks, thats the discussion, but still no answer in there. Mmmm...if we could just see the tech drawings of the air pipe ducting system