Here in the South, quite a bit of any car trip in the summer with anybody in the backseat is spent with some of the front vents directed to the rear - either with the fan set to high, or, if there's a front passenger and the fan soon has to be turned down, several vents aimed to the rear for a longer time.
We're buying our first new car in a long time (incidentally, in the family of the car being replaced, only the much more expensive top version had rear vents, and I never spent the $$$ and effort to retrofit).
The few other cars we're looking at all have rear vents. We've now dropped the Sonata from consideration (the "snazzy" styling has already gotten old, without even owning one...), but a Chrysler 300, for somewhat less than TDI/DSG money, is still an alternative.
Given how much cheap interior luxury has come along since the last time we bought a new car, if I'm going to spend new-car money, I really don't want to compromise on something like this which affects the comfort of every trip that much.
The only reason the lack of rear vents isn't a deal breaker is that I feel able to retrofit it in some manner, and hopefully soon.